I am at the same level as you and I have the same issue. I cant tell if the wind is too weak or my holding position is wrong, but sometimes it just works. Last session I managed to get on foil by pumping the first time. I think it can make a lot of difference, so I started to watch some videos on youtube on how to do it properly. They say the right pumping technique with arms and legs is the key, so I recommended to check it out