Having the same issue, docker says there is an update, on version 1.18.4.2171, tell it to update and get the following:
Pulling image: linuxserver/plex:latest
IMAGE ID [latest]: Pulling from linuxserver/plex.
Status: Image is up to date for linuxserver/plex:latest
TOTAL DATA PULLED: 0 B
Where is the container log located by chance? I know when I click on log next to the docker, there isn't much in there.