Judging by the timestamp on @DarthCoin's post below he was probably the first. I didn't dig into it until I was tasked with writing a ~20 page technical report on Muun and comparison with others last fall. There's a lot of problems and while they are good guys, there's reasons for the warnings and this was it.

There's been way bigger problems than people know about either. I am not pilling onto the debate rn, it's up to others to figure it out now.