There's just single or double oak log blocks everywhere instead of large oak trees. Noticed this in Forest, Jungle and Jungle Edge biomes so far. Also tried to grow large oaks with bone meal, which gives the same result, so I assume this is a general issue with this type of tree.
After further invesitgation, we can tell that the stumps are actually the so-called "balloon oak" variant generating upside down. They only generate leaves when air is underneath though, as sometimes visible in caves. The following superflat preset shows the issue very well:
The actual large oak trees with branches don't seem to generate at all, this issue was moved to ticket