Thanks for the logs - forum user @millerim has shared the script he used for capturing memory usage every minute and recording the time to 1 second accuracy . Could you look into adapting this for your setup.
See this post Server Crashes While Loading EPG Data - #12 by millerim
Run a script like it after restarting the server and finding the PID for the plex media server process
Download server logs periodically - say twice or three times a day
Once you reach high memory usage levels and the memory stays high, then capture logs and attach the memory snapshots text file ( please make sure date and time shows time including seconds ) and all the saved zipped server logs and the latest zipped logs
