Having a really strange issue on the forum

Twice now, I've replied to a recent thread and the post hasn't gone into the intended thread. Instead it went into a random necro thread on a completely different forum. Once was a mid 2000's football thread, then a WTB in the GTO forum again nearly 10 years old

Usually posts, go as intended, but this is really strange

Anyone heard of this before/experienced this?

 

It looks like you have related threads turned off, however, that setting does not work for mobile. So are you using mobile and, possibly, scrolling down and replying to a related thread?

Besides that, I'm not aware of this being an issue. It's very unlikely to occur without being on the wrong thread.