fixed now (but I don't know how long this duct tape will last)

I don't have much to go on, but it looks possible that you submitted on your phone, and lost connection part way through submitting (it looks like a mobile data IP). Your phone connected to your wifi a bit later, and at that point it retried the submission. The forum retries once on failure, but I think this was actually caused by Safari retrying later once you got a connection and opened the page (which would have been displaying a "failed to connect" error) again.