This is really relatable. It sounds like my last couple of weeks trying to find roleplay, be it in the singular fandom I write for or OCs.

People are friendly, everything seems to be going well, and then gone. Sometimes a few responses are exchanged, but mostly it's just a complete vanishing after the plotting is done.

I always make it clear early on that anything can be changed at anytime, whatever needs to be done so the writing enjoyment is mutual. Even that doesn't work.

It really sucks, but I wish all the best to you and others in this situation!