Yep same here. I went to the docker main page and noticed this comment:
"Hey, I saw that plex download has changed its url. It was https://downloads.plex.tv/ and now its https://plex.tv/downloads
Whe you restart the container plex is not starting since its in a loop redirecting to the URL.
Please upgrade it."
This does seem to be true as the first URL now does a redirect to the new URL. I assume we wont be getting any new plex updates until that is fixed in the docker image.