Hey, I got it working in the end. Turns out the reason for the issue with the “page cannot be reached” was cause of Lets Encrypt’s re-certification limit of 5 in a week, so that was my mistake and the page I was seeing was just cached.
In the end I reinstalled the forum, and luckily had a pretty recent backup so I just restored that through the command, and then reinstalled my old plugins. And I also upgraded my the server to 8gb RAM since I might use it for other things and now the forum is all good, no more 137 exit codes. Working great now.
Cheers for all the topic help! 