Hello,
we've had the same problem after migrating from 7-Mode to cDOT using the 7-MTT.
Are the share-properties "showsnapshot" and "show-previous-versions" set on your shares?
It seems that these attributes are not migrated by the 7-MTT.
You can check this like this:
share properties show -vserver <vserver-name> -share-name <share-name>
If the options are not set, you can set them using the following commands:
share properties add -vserver <vserver-name> -share-name <share-name> -share-properties showsnapshot
share properties add -vserver <vserver-name> -share-name <share-name> -share-properties show-previous-versions
Afterwards the explorer.exe has to be restarted.
We had to add "showsnapshot" AND "show-previous-versions", one of them was not enough.
This was the solution in our case, hope that it'll help you too.