Rob,

This is the response I got from our IT guy with respect to our system.  We we're moving from SBS 2008 R2 to WS 2019:

....it had to do with the “Item-level targeting” section of the mapped drives group policy.  There is an option that never worked properly in previous versions of Windows Server, but was finally “fixed” in the more recent versions.  I can’t remember exactly, but I think it was the option for “Apply once and do not reapply” option that needed to be selected so that the policy would not try to re-map the drive while the use is in-session.  This would need to be the same across all mapped drives in order to prevent the re-mapping."

Apparently worked for us.....but results may vary.  If you search for "Apply once and do not reapply" you probably find it.