Hello Bristow.
I faced a file sharing SNAFU between several PCs all using U/M which may be similar to your problem in some ways.
My conclusion is that open file sharing has been made into an arcane part of the Linux ecosystem in general, and good, clear info is almost non-existent.
I solved this problem by using SSHFS after posting about this here at this forum and doing a tremendous amount of testing, searching & reading about samba, NFS and anything else I was able to find.
Here is my thread about this subject:
Searching at this forum does also reveal quite a few mentions of SSHFS, but my path into it did not come from here at all and I do have some saved notes about the process used in case I need to be reminded how it was done at some future date.
Best Wishes for Success !!