The latter is supposed to happen.. it is fun

Don't sheet out and try to slow, that is what caused the instability. As soon as you sheet out the sail power is no longer holding the front of the board down.
You may also be over finned, most people are when it is really windy, and that won't help
I know it is different for freeride, but as a 90kg guy, on my wave gear if it is 25-30kn I am on 80L and 4.7. In constant 35 (real
solid 35, not gusting 35) I am on 4.0 and 75L.
You are fighting volume and sail saize (and probably fin size too) in those gusts man