Okay I actually think things are getting better. Looking in your latest Plex Media Server.1.log I am not seeing the errors from before. This log now looks good (at least to me)!
At this point could you optimize database and clean bundles via settings → manage > troubleshooting.
Then, take 1 movie which is causing you a problem and do a full plex dance with it.
Once its matched again after the dance try and set a poster.
