It's happened on mine and also for another members with whom I've previously spoken to via PM.....threads locked for seemingly no reason. No explanation and a rather abrupt halt to a conversation.
For example, my thread about a north London meet up has been locked up by an admin. No explanation and another thread to bring the event back up was deleted. Again this was just done. No other thread on the events page is locked. Kinda pointless me spending all the time I have done trying to organise it when any attempts to organise is prevented.
Suggestion is a one line reason as to why a thread is locked :)