A couple of points/questions:
1) You can check what build you're using at Options > Help > About MediaMonkey (based on the May 4 date, it sounds like you're using build 1080).
2) This might be a variant of
https://www.ventismedia.com/mantis/view.php?id=20007 which was fixed in build 1080 . Did you ever see any warnings in MMA along the lines described in that bug?
3) It might be related to another issue that's been observed on occasion before with lineage OS:
- Tap 'Grant' in MMA
---> The folder selection dialog opens allowing for selection / access permission grant to the folder
- Tap 'Use this folder' and then 'Allow' to grant access to each folder
---> The main screen that shows which folders have been granted access fails to update! As far as we've been able to tell, this occurs occasionally if the Android system isn't responding correctly to the permisions request despite having granted permission.
Have you observed anything like this as you're granting access to folders?
4) Last question: I assume that the answer to all of the items below is 'yes', but to be sure: did you successfully:
a) Grant access to the /MediaMonkey folder (Step 1)?
b) Allow MediaMonkey to access photos and media on your device (Step 2)?
c) Grant access to _all_ of the various media folders on your device (Step 3)?
Also, I see you sent the debug log--thanks!
-Rusty