I tried this on another computer with the same results.
Overview: Windows 10 (multiple computers), Turned Virus Protectors off, JRiver 29.0.86. Using JRiver for 12 years.
A quick overview of my testing (which you could easily duplicate)
Backup current JRiver DB (100,000+ files)
Clear Library - so that I'm starting fresh
Copy one music directory over to root directory of USB Drive (F:) example F:\Bob Seger - Night Moves
Import that Directory as Media Sub Type = Music or Audiobook
Check fields to make sure that they are set up for write access - under tools, options modify library fields (Artist, Name, Track #, Disc #, Genre). Check JRiver to make sure that it will write tags (see screens above)
Modify fields using JRiver Tag option (Artist, Name, Track #, Disc #, Genre) etc.
Even though the fields should be written to when modified then I do : right click, Update tags (from Library)
Check files at windows level and 3rd party app (Tag&Rename) - NO MODIFIED FIELDS ARE UPDATED
If I do select Update Library (from tags) it will update JRiver but JRiver WILL NOT WRITE TAGS TO FILES. Tested both MP3 and FLAC files.
Can someone please confirm that following this logic they are able to write tags to files and that it works for them?