@Squarehead speaks good advice..
On the odd occasion I have had similar happen to me, I have let that 1st coat, nearly set, then (controversial), give it a rub with a sponge then 2nd coat as normal.......obviously, as I am brill this doesn't happen often...lol
So come on you lot? What happened I glue it about a week ago and skim all the other wall no prob but had to do other things so this wall go left , so this morning I put a tight coat of pva on just in case wall went tacky put it on fine as normal than bang went to flatten with plazi than the s**t hit the deck! The plastering was slipping everywhere!! Everywhere!and the glue was actually bleeding through!!!???
The wall probably had wall paper on it before the pva makes the old wall paper paste like mushy silicon the skim just slides on it once it starts to firm up
U have to wait for it to totally dry can take a while though a good hour or two