First of all thanks for the quick reply.
So i just grown 25 rubber trees with bonemeal, but all of them had this same issue, so i really don't think it's just badluck.
However i was wrong at something:
As i said before when they grow they sometimes already have resin on them and after harvesting that resin i can spam treerap on that face and get more resin for a while(until the hole breaks i guess), so i guess there is a resin hole on those.
Also i don't know if it has anyhing to do with all of this but sometimes rubbertree grows way too short.
By short i mean one or two blocks of rubberwood and some leaf, then again it happens only sometimes.