Twice I’ve tried to post in the “how high can we go” thread and it goes to a white page and says “error 502 bad gateway”
how high were you when you tried it? 
…sea level…
No joke it did happen it could just be our desk top… But… It happened… It did,
502s have nothing to do with something like a post count. The forum software doesn’t go “holy crap, what a FAT thread! I don’t know what to do with it!”… it’s almost completely agnostic to the number of pages. Thread content is stored in a database, and the software has a query that says something like, “based on this user’s preferences, I need 25 entries, starting at entry 475.” Then it grabs the 25 entries and renders them into a webpage.
It is no more difficult for the software to do this than to grab 25 entries from a 1-page thread.
502 is just a bad connection of some sort. It’s either coincidence that it was in the high post count thread when you encountered it, or there’s a tiny TINY chance that the back end (web server) is reporting back the wrong error code. The most likely explanation is that it is in fact a 502.
Yeah I didn’t think it had anything to do with which specific thread it was in just wanted to point out specifics. 
Later in the evening I got some 502s as well. Seemed to pop up under the same circumstances each time for me as well (searching for a particular thread). It actually didn’t “feel” like a true bad gateway. The hosting provider might have a flaky server. :-/ They did perform some sort of upgrades/changes recently.