Is it because you usually have less power after the session than before surfing? Could be! Every windsurfer knows the problem of not being able to turn the base plate. However, the fact that (stronger) helpers or appropriate tools are not always on hand is no longer a problem, because with a little trick you can easily loosen a jammed mast base plate yourself.
You can see the exact procedure in the picture gallery at the beginning of the article - so if you get stuck again, give it a try!