Drafting .mi objects downloaded into workspace are always outdated

Hi,
we're still using Drafting 20.4 on some virtual machines, connected to the Workgroup Manager of Windchill 12.0.2.0. Just for some users - although the server is set and available, the workspace is new and incorrupted, Drafting is correctly set as application, the cache is low, etc etc... - all the .mi objects downloaded into workspace are always outdated, and the synchronization has no effect on this. So Drafting doesn't open anymore any .mi drawing. I've already tried to erase the server ad set it again, same result.