Minecraft Version: 1.12.2
Forge Build: 2555
Mod Version: 0.7.2c

When attempting to grow acacia trees in Savanna biomes they don't grow beyond this point; https://imgur.com/nY4IukG . I've waited hours without the trees changing from this state. I've attempted replanting them, and planted 10 trees to compare to see if any of them would grow; nothing. I've changed the growth rate to be higher then replanted trees, and I've changed the growth rate to be lower and replanted trees; same results.

I've tested oak on plains, and that grows just fine into larger trees at any growth rate. I haven't tested any other tree types in other biomes though.

Okay, I've run some more tests, and the problem appears to happen to every tree on a server, but in single player all trees grow normally.

Leaves appear to grow and decay on occasion, but the tree branches don't get any longer and the tree doesn't get any taller.

When I ported to 1.10+ the naming changed for whatever is now isFullBlock(). I was mistakenly using isOpaqueBlock() which behaves differently on dedicated server. Fixed.

I can confirm your results. This has top priority for a fix. Thanks for pointing this out.

Even more strange.. If you break a few leaves blocks on the short tree then it will start growing past that stage. But it's not growing normally.