I do not know how to reproduce it

When I place for example some grass on grass blocks and I destroy the grass blocks grass stay floating like if it was normal, I can't even activate a lever. Water doesn't flow...

Only things in my world (created in 20w45a) are a amethyst duper and a try to make a real farm. The computer I use is not as good as the one I use the rest of the time (I'm only at 30 FPS and less when the duper runs) 

When I reload my world It's like I didn't do anything and everything remains as when my world was normal but it still does the same thing

The weird thing is that it seems to be lag but there is nothing running in the background or in the world

On my better computer that re-appened with 1700ms per tick with nothing impoertant on the backgroung

Actually was a problem with randomTickSpeed too high up (might still be a bug but not this one...). So it might be a duplicate but I searched a bit and didn't find an opened issue for really high randomTickSpeed lag.