I've solved my problem, after i noticed that it only occurred with Flac files.
MP3 tags treat ratings differently. I can solve this by changing the rating value for flac files in Foobar using a different scale (1 - 100) 10 = 1 star, 100 = 5 stars.
Previously I was giving flac files a rating of 5 which mediamonkey interpreted as 0.25 hence too low for any stars.

Please provide a sample file to support: https://www.mediamonkey.com/support

You need to upload to a Cloud Service and include the link to the shared file(s) in your Support Ticket. Also indicate what Rating value you expect.

Flac files
I've just deleted the files from the MM database & readded them. Same result, no rating

Do copies of those 2 files scan in with the correct Rating? Also what File Type(s) are affected?

Build 3222
I've only noticed two so far. Previous files with ratings appear correctly. Maybe something happened between builds?

Which Build (Help > About) of MediaMonkey are you using, and presumably you have issues with files already in the MediaMonkey Library.

Files are tagged correctly in Foobar 2000 using numerics 1 - 5 then added to MM. Previously MM would detect the tag & convert numeric to Stars ie 5 = 5 stars. This is not happening now. Ratings tag is blank