Exception: Message Saving Error while dowloading calendar from Exchange web services (C# .NET)

Hi team,
I am facing an issue, when i am downloading and uploading Appointments from a calendar folder into another exchange account. it throws an Exception :
Message Saving Error ::The send or update operation could not be performed because the change key passed in the request does not match the current change key for the item., Item could not be saved because conflicts were detected when saving. ItemId:RgAAAAD+0XMxUuYVQIBrcgpdcZV4BwCRLGTpYvmETa3da5qNk/LOAAAUHhALAACRLGTpYvmETa3da5qNk/LOAAAUHvCgAAAPSaveStatus: IrresolvableConflict
PropertyConflicts:
Property = TextBody, values = <Original:, Client:Property: [0x1000001f] TextBody, PropertyErrorCode: NotFound, PropertyErrorDescription: ., Server:Property: [0x1000001f] TextBody, PropertyErrorCode: NotFound, PropertyErrorDescription: .>, ResolvedValue = Property: [0x1000001f] TextBody, PropertyErrorCode: NotFound, PropertyErrorDescription: ., ConflictResolvable = True
Property = ClientIntent, values = <Original:, Client:0, Server:0>, ResolvedValue = 0, ConflictResolvable = True
Property = RtfBody, values = <Original:, Client:Property: [0x10090102] RtfBody, PropertyErrorCode: NotFound, PropertyErrorDescription: ., Server:Property: [0x10090102] RtfBody, PropertyErrorCode: NotFound, PropertyErrorDescription: .>, ResolvedValue = Property: [0x10090102] RtfBody, PropertyErrorCode: NotFound, PropertyErrorDescription: ., ConflictResolvable = True
Property = AppointmentStateInternal, values = <Original:, Client:1, Server:0>, ResolvedValue = , ConflictResolvable = False
Property = OutlookVersion, values = <Original:, Client:15.20Ex, Server:15.20Ex>, ResolvedValue = 15.20Ex, ConflictResolvable = True
Property = OutlookInternalVersion, values = <Original:, Client:134479874, Server:134479874>, ResolvedValue = 134479874, ConflictResolvable = True
Property = AnnotationToken, values = <Original:, Client:Property: [0x10170102] AnnotationToken, PropertyErrorCode: NotFound, PropertyErrorDescription: ., Server:Property: [0x10170102] AnnotationToken, PropertyErrorCode: NotFound, PropertyErrorDescription: .>, ResolvedValue = Property: [0x10170102] AnnotationToken, PropertyErrorCode: NotFound, PropertyErrorDescription: ., ConflictResolvable = True
Property = BigFunnelCorrelationId, values = <Original:, Client:2577a063-670a-4b9b-b2ba-da8a20f846c2, Server:2577a063-670a-4b9b-b2ba-da8a20f846c2>, ResolvedValue = 2577a063-670a-4b9b-b2ba-da8a20f846c2, ConflictResolvable = True
Property = BigFunnelIndexingStart, values = <Original:, Client:Property: [{0b63e350-9ccc-11d0-bcdb-00805fccce04}:‘BigFunnelIndexingStart’] BigFunnelIndexingStart, PropertyErrorCode: NotFound, PropertyErrorDescription: ., Server:Property: [{0b63e350-9ccc-11d0-bcdb-00805fccce04}:‘BigFunnelIndexingStart’] BigFunnelIndexingStart, PropertyErrorCode: NotFound, PropertyErrorDescription: .>, ResolvedValue = Property: [{0b63e350-9ccc-11d0-bcdb-00805fccce04}:‘BigFunnelIndexingStart’] BigFunnelIndexingStart, PropertyErrorCode: NotFound, PropertyErrorDescription: ., ConflictResolvable = True
Property = BigFunnelMessageUncompressedPOIVersion, values = <Original:, Client:9, Server:9>, ResolvedValue = 9, ConflictResolvable = True
Property = BigFunnelPOIIsUpToDate, values = <Original:, Client:True, Server:True>, ResolvedValue = False, ConflictResolvable = True
Property = BigFunnelPOIContentFlags, values = <Original:, Client:2047, Server:2047>, ResolvedValue = 2047, ConflictResolvable = True
Property = BigFunnelPoiNotNeededReason, values = <Original:, Client:0, Server:0>, ResolvedValue = 0, ConflictResolvable = True
Property = IndexingAttemptCount, values = <Original:, Client:Property: [{0b63e350-9ccc-11d0-bcdb-00805fccce04}:‘IndexingAttemptCount’] IndexingAttemptCount, PropertyErrorCode: NotFound, PropertyErrorDescription: ., Server:Property: [{0b63e350-9ccc-11d0-bcdb-00805fccce04}:‘IndexingAttemptCount’] IndexingAttemptCount, PropertyErrorCode: NotFound, PropertyErrorDescription: .>, ResolvedValue = Property: [{0b63e350-9ccc-11d0-bcdb-00805fccce04}:‘IndexingAttemptCount’] IndexingAttemptCount, PropertyErrorCode: NotFound, PropertyErrorDescription: ., ConflictResolvable = True
Property = IndexingBatchRetryAttemptCount, values = <Original:, Client:Property: [{0b63e350-9ccc-11d0-bcdb-00805fccce04}:‘IndexingBatchRetryAttemptCount’] IndexingBatchRetryAttemptCount, PropertyErrorCode: NotFound, PropertyErrorDescription: ., Server:Property: [{0b63e350-9ccc-11d0-bcdb-00805fccce04}:‘IndexingBatchRetryAttemptCount’] IndexingBatchRetryAttemptCount, PropertyErrorCode: NotFound, PropertyErrorDescription: .>, ResolvedValue = Property: [{0b63e350-9ccc-11d0-bcdb-00805fccce04}:‘IndexingBatchRetryAttemptCount’] IndexingBatchRetryAttemptCount, PropertyErrorCode: NotFound, PropertyErrorDescription: ., ConflictResolvable = True
Property = IndexingErrorCode, values = <Original:, Client:Property: [{0b63e350-9ccc-11d0-bcdb-00805fccce04}:‘IndexingErrorCode’] IndexingErrorCode, PropertyErrorCode: NotFound, PropertyErrorDescription: ., Server:Property: [{0b63e350-9ccc-11d0-bcdb-00805fccce04}:‘IndexingErrorCode’] IndexingErrorCode, PropertyErrorCode: NotFound, PropertyErrorDescription: .>, ResolvedValue = Property: [{0b63e350-9ccc-11d0-bcdb-00805fccce04}:‘IndexingErrorCode’] IndexingErrorCode, PropertyErrorCode: NotFound, PropertyErrorDescription: ., ConflictResolvable = True
Property = IndexingErrorMessage, values = <Original:, Client:Property: [{0b63e350-9ccc-11d0-bcdb-00805fccce04}:‘IndexingErrorMessage’] IndexingErrorMessage, PropertyErrorCode: NotFound, PropertyErrorDescription: ., Server:Property: [{0b63e350-9ccc-11d0-bcdb-00805fccce04}:‘IndexingErrorMessage’] IndexingErrorMessage, PropertyErrorCode: NotFound, PropertyErrorDescription: .>, ResolvedValue = Property: [{0b63e350-9ccc-11d0-bcdb-00805fccce04}:‘IndexingErrorMessage’] IndexingErrorMessage, PropertyErrorCode: NotFound, PropertyErrorDescription: ., ConflictResolvable = True
Property = IsPartiallyIndexed, values = <Original:, Client:False, Server:False>, ResolvedValue = False, ConflictResolvable = True
Property = IsPermanentFailure, values = <Original:, Client:Property: [{0b63e350-9ccc-11d0-bcdb-00805fccce04}:‘IsPermanentFailure’] IsPermanentFailure, PropertyErrorCode: NotFound, PropertyErrorDescription: ., Server:Property: [{0b63e350-9ccc-11d0-bcdb-00805fccce04}:‘IsPermanentFailure’] IsPermanentFailure, PropertyErrorCode: NotFound, PropertyErrorDescription: .>, ResolvedValue = Property: [{0b63e350-9ccc-11d0-bcdb-00805fccce04}:‘IsPermanentFailure’] IsPermanentFailure, PropertyErrorCode: NotFound, PropertyErrorDescription: ., ConflictResolvable = True
Property = LastIndexingAttemptTime, values = <Original:, Client:7/10/2019 12:16:04 PM, Server:7/10/2019 12:16:03 PM>, ResolvedValue = 7/10/2019 12:16:04 PM, ConflictResolvable = True
Property = ErrorTags, values = <Original:, Client:Property: [{0b63e350-9ccc-11d0-bcdb-00805fccce04}:‘ErrorTags’] ErrorTags, PropertyErrorCode: NotFound, PropertyErrorDescription: ., Server:Property: [{0b63e350-9ccc-11d0-bcdb-00805fccce04}:‘ErrorTags’] ErrorTags, PropertyErrorCode: NotFound, PropertyErrorDescription: .>, ResolvedValue = Property: [{0b63e350-9ccc-11d0-bcdb-00805fccce04}:‘ErrorTags’] ErrorTags, PropertyErrorCode: NotFound, PropertyErrorDescription: ., ConflictResolvable = True
Property = ErrorProperties, values = <Original:, Client:Property: [{0b63e350-9ccc-11d0-bcdb-00805fccce04}:‘ErrorProperties’] ErrorProperties, PropertyErrorCode: NotFound, PropertyErrorDescription: ., Server:Property: [{0b63e350-9ccc-11d0-bcdb-00805fccce04}:‘ErrorProperties’] ErrorProperties, PropertyErrorCode: NotFound, PropertyErrorDescription: .>, ResolvedValue = Property: [{0b63e350-9ccc-11d0-bcdb-00805fccce04}:‘ErrorProperties’] ErrorProperties, PropertyErrorCode: NotFound, PropertyErrorDescription: ., ConflictResolvable = True
Property = ItemVersion, values = <Original:, Client:4, Server:3>, ResolvedValue = 4, ConflictResolvable = True
Property = ChangeList, values = <Original:, Client:System.Byte[], Server:System.Byte[]>, ResolvedValue = System.Byte[], ConflictResolvable = True
Property = MiddleTierProcessName, values = <Original:, Client:w3wp, Server:MSExchangeMailboxAssistants>, ResolvedValue = w3wp, ConflictResolvable = True
Property = ClientInfoString, values = <Original:, Client:Client=WebServices;UserAgent=[NoUserAgent];, Server:Client=EBA;Action=EntityExtractionCalendarItem;EntityExtractionCalendarItem>, ResolvedValue = Client=WebServices;UserAgent=[NoUserAgent];, ConflictResolvable = True
Property = ResponsibleUserName, values = <Original:, Client:/o=First Organization/ou=Exchange Administrative Group(FYDIBOHF23SPDLT)/cn=Recipients/cn=00067FFE0968B8B5, Server:/o=ExchangeLabs/ou=Exchange Administrative Group (FYDIBOHF23SPDLT)/cn=Configuration/cn=Servers/cn=TY2PR0101MB2399/cn=Microsoft System Attendant>, ResolvedValue = /o=First Organization/ou=Exchange Administrative Group(FYDIBOHF23SPDLT)/cn=Recipients/cn=00067FFE0968B8B5, ConflictResolvable = True
Property = MailboxDatabaseName, values = <Original:, Client:/o=ExchangeLabs/ou=Exchange Administrative Group (FYDIBOHF23SPDLT)/cn=Configuration/cn=Servers/cn=SIXPR01MB0319/cn=Microsoft Private MDB, Server:>, ResolvedValue = /o=ExchangeLabs/ou=Exchange Administrative Group (FYDIBOHF23SPDLT)/cn=Configuration/cn=Servers/cn=SIXPR01MB0319/cn=Microsoft Private MDB, ConflictResolvable = True
Property = OriginalLastModifiedTime, values = <Original:, Client:7/10/2019 12:16:04 PM, Server:7/10/2019 12:16:03 PM>, ResolvedValue = 7/10/2019 12:16:04 PM, ConflictResolvable = True
Property = HtmlBody, values = <Original:, Client:, Server:>, ResolvedValue = , ConflictResolvable = False
Property = BigFunnelPOIUncompressed, values = <Original:, Client:, Server:>, ResolvedValue = , ConflictResolvable = True

but the mails are saving as well.

@pradeepnegi,

I have observed the stack trace shred by you and request you to please share the working sample code along with test account credentials that we may use to verify and resolve the issue on our end. Please share the requested information so that we may proceed further to help you.