Could also be that there is something hanging on the bottom of the hull that is causing the prop to ventilate, or there is an issue with the trim on the motor, although I suspect you would notice if it was not trimming down all the way.

Had that problem a few months ago, was running into a heavy chop and had the motor trimmed way up, when I turned to go with the waves, the prop immediately blew out at anything more than idle speed. Took me a few minutes to figure it out, but as soon as I trimmed down it went back to normal.