I experienced some problems with water and lava when I was a bit far (I wouldn't call it far) from the spawn. I tp-ed myself to X10000, Z10000 and I placed water and lava on the floor. The problem is that it took it too much time to flow. Most of the times it just stays just where I put it and it doesn't flow at all.

I tried to change the new option "Priority Updates" in case it had something to be with that, but it didn't help.

Another interesting thing is that the debug command returned stable 20tps, and entities move and react fine, the problem is only about water and lava flow.