My Plex server is suddenly no longer accessible in the web player

I am still having this issue a few months on, with no luck fixing it.

I seem to not be the only one, I think this post describes the same issue. Unfortunately the provided solution has not worked for me:

I am also wondering if these posts are regarding the same issue:

In short, looking through the forums it seems like lots of people are having the same issue, and I am surprised this hasn’t been resolved by Plex yet. They obviously made a change that has broken something for some people.