Thanks a lot for reporting the issue!
If you are not sure about config.txt just attach it here and I'll have a look
In general I add settings at the end of config.txt as that makes sure they override any previous settings.
BTW: it could be that one of the other config.txt settings I mentioned helps with your RPi, please test those, too (try only one of them at a time).
And please tell us which RPi you are using (2B, 3B, 3B+) and post a logfile of LE 9.2.3 running with the replaced firmware files. Go to Settings -> LibreELEC -> System and select "Upload latest Kodi log and configs, and view the short URL", then post the URL you got.
so long,
Hias