Every rubber tree i grow myself (from saplings) doesn't have any resin hole at all.
Resin doesn't spawn on them overtime and i can't get resin out of them no matter how much i use the treetap so i am assuming they don't have a resin hole.
When they grow they sometimes grow with resin on them, however after harvesting that resin, again it acts as if there is no resin hole.
And this only happens with trees that i grow. Naturally spawned ones work fine.