I'm seeing a lot of instances lately where, if I try to post a new thread or a reply on an existing thread, it hangs for a while then gives me a "504 Gateway Timeout". Afterwards, when I look, I see that my post was posted, but the forum listing (where it shows the "last post by" information) gives no indication that anything has been posted. It looks like this is not happening to just me, since I see a lot of threads where it shows something in the "last post" information, but if you look at the actual thread, you see there are one or more replies that were posted after the "last post" shown in the forum listing.
Once a cause is identified and fixed, should the forum indexes be rebuilt? Yeah, I know that's a time-consuming and somewhat disruptive operation, but given how widespread the effect of this seems to be, it might be worth it.
P.S. I'm primarily using the mobile version of the site, if that makes a difference.