Access 'profile name' folder. If any of the 'prefs.js' files have a size of 0, delete them.
As a test:
rename prefs.js (currently the one in use) as prefs-5.js to keep and rename prefs-1.js (assuming it has a size >0) as prefs.js.
start Thunderbird to see if 'prefs-1', now 'prefs.js' works.
You may need to repeat this action to test other 'prefs.js' files. So if the renamed 'prefs-1' (now prefs) does not work, rename it back to 'prefs-1.js' and then rename 'prefs-2.js' as 'prefs.js' etc. Exiting Thunderbird each time before you need to access 'profile name' folder.
If you find one that works, you can delete all those that do not.
Please report back on results after renaming and testing each of the numbered prefs files.