Strangely enough, I just experienced a couple of errors.
What happened: as normal, I visited the site and scanned the list of new posts. Opened page 1 of this thread (in a new tab) and read the new-to-me postings. When I tried advance to page 2, it 'hung' for about 2 minutes before reporting a "522" error, see pdf attached.
After a couple more minutes, I was able to access the site and open this thread (to post this reply). [See below; could not post initially.]
My system: yes, I use an old version of Safari (10.1.2 from circa 2017) on OS X (10.10.5). I have reasons that are holding me back from updating to new versions. There are a couple of sites that refuse to connect with my version of Safari (notably hobby-machinist.com). For those, I use Firefox...but I strongly prefer Safari. I figure since my bank, BMO, is OK with the security on this version of Safari, it can't be that bad.
Update: I spent about 20 minutes trying to post this message. Upon clicking the "Post Reply" button, the animation indicating that the site was working would appear for a few seconds. However, the page would not reload or otherwise show that my message had actually been posted.
Trying to access the thread in a new tab produced a "525" error a few times, see attached.
Craig