Player placed leaves decaying

Did you disable the vanilla data pack ?

I haven't disabled anything. I updated to the new 1.13 pre-release, signed into my account, signed into my server and then leaves that I had placed all over my minecraft town started decaying. I had the same issue with 18w22a, 18w22b and 18w22c.

I should also mention that I switched back to 18w21b and the issue stopped. I was able to place leaf blocks again without them decaying.

18w21 corrupted the world.
The issue should be resolved when you restore a pre-18w21 backup or load the 1.12.2 world.