Here is another version of the test code. It adds code to demonstrate the date error on some of the items in the US Holidays folder
Thank you for posting your inquiry.
We have investigated the issue at our end and the problem seems to be specific to specific appointments from the US Holidays folder. These 3 ICS files are as attached here for reference as well. If we just use MailMessage and then MapiMessage.FromMailMessage, the issue is reproduced which shows that it is not related to EWS. The issue has been logged as EMAILNET-38746 for further investigation by our Product team. We’ll update you here once there is more information or a fix version available in this regard.