I am just running the sample code project. “CreateLayerGroups”. The PSD saved cannot be opened from Photoshop 2019 and Clip Studio Paint.
I have observed the issue shared by you and request you to please provide the generated output file along with snapshot of issue when opening in Photoshop 2019 and Clip Studio Paint. We will be able to proceed further with investigation on our end on provision of requested information.
Note that the PSD file is generated from your own Sample Project as mentioned in 1st post. Not my custom code. That may be related to LayerGroup.
Thank you for sharing the requested information with us. An issue with ID PSDNET-542 has been created in our issue tracking system to further investigate and resolve the issue. This thread has been linked with the issue so that you may be notified once the issue will be fixed.