Try this:
https://support.plex.tv/articles/202967376-clearing-plugin-channel-agent-http-caches/
I did it recently.
It worked as advertised.
Before that - do this:
With LMA in priority, Embedded Titles within MP4/M4V files are preferred - even over a perfect file name. Local Media Assets should - AT ALL TIMES - remain enabled (unless specifically instructed to turn it off).
Local Media Assets should be ‘Demoted’, to the bottom of the stack of active agents under ALL tabs in Shows and Movies, but should NOT be disabled.
Local Media Assets is needed for many things - it doesn’t need to be given Tip-Top-Priority (as Plex has so hatefully placed it as it’s …
In case that internal metadata you don’t need in those MP4 files starts making your life miserable. Plex matches via File Name. Name your files properly. Jettison all the junk.