A known phenomenon with ATR's is that after de-icing the stabilizer the gap can become blocked.
The procedure here is to keep pulling because it WILL fly and it will be normal from there on. You just have to increase the elevator angle until it blows through the gap.
My company experienced this and after meeting with the ATR people introduced the procedure that...the horizontal stabilizer shall always be de-iced as if it were covered with clear ice... thus the sludge gets blasted.
There has been no recorded incident since, to the best of my knowledge.