LMS on Debian. Quick search problems and content scan dying

Platform: Debian (first Jessie, now Buster/Sid)
LMS: 7.9.1, now 7.9,2

LMS on my Debian home server had been stable for a long time, but recently started having problems.

The first symptom was that the Quick search function in the GUI stopped working. It produced no results, but the full search still worked.

Then I realised that my Playlists weren't being picked up by the content scan any more, and when I looked closer I realised that it looked as if the content scan was failing part way through and not completing (the GUI front page says "scanning media library" continually).

I found some reports on this forum of similar problems (at least as regards the quick search), but without any details on what the underlying cause might be. I tried removing LMS 7.9.1 and then installing 7.9.2, but that brought back all my existing config (so it clearly didn't clear all the stored data down) and the same problems occurred.

I'm guessing I will have to completely wipe the installation and all the config files I can find and start again, but before I do I thought I'd try to do some digging and see if I can provide some info so maybe the knowledgeable here can get some clues on what's going on.

Observations so far

1. The quick search issue appears to be linked to errors in the scanner log file complaining that a database table was missing. Annoyingly I lost the copy of the scanner logfile that showed the error, and the missing table name, because one of the OTHER symptoms is-
   
2. After a period of a few minutes with the scan stuck, the server is sometimes deleting the content of both the server.log and scanner.log files. I have seen both files end up as 0 bytes in size when they contained many lines just a few minutes before.
   
   If I stop/start the server and initiate a scan, it scans the Music and Podcast folders, and then seems to choke as it never gets to reading the Playlists folder, and the "abort scan" link stays active.
   
   At this point, in the scanner.log file the last few lines are-
   
   
   Code:

   ---

   [19-03-23 00:13:18.6435] Slim::Utils::Scanner::Local::__ANON__ (374) Scanning new audio files (382)
[19-03-23 00:13:20.5676] Audio::Scan::scan (64) Warning: Error: Unable to read at least 4 bytes from file.
[19-03-23 00:13:29.7482] Audio::Scan::scan (64) Warning: Error: Unable to read at least 4 bytes from file.
[19-03-23 00:13:29.7504] Audio::Scan::scan (64) Warning: Error: Unable to read at least 4 bytes from file.
[19-03-23 00:13:29.8003] Slim::Utils::Scanner::Local::__ANON__ (454) Rescanning changed audio files (0)

   ---

   This looks significant, but it would help if the software told you WHICH file(s) it couldn't read at least 4 bytes from!

Any ideas on more debugging that can be done at this point, or do I just have to nuke the install and start again?