I was playing around in 21w10a and I was terraforming a mountain. I tried to get grass to spread faster so I turned up the RandomTickSpeed and nothing happened. I thought It wasn't high enough so I raised it even more to 10000000 I think. at first nothing happened so I waited a while and went to work on another thing. then the first noticeable problem happened. a few items fell on the ground and I wasn't able to pick them up. then, I tried dropping items and it would delete them instantly. I went around and tried looking for other problems and the only other one I could find was that falling blocks acted like solid blocks. after that the game got really choppy and I decided to quit, but to no avail as it was on the Saving World... screen for 15 minutes. there may be more problems that I wasn't able to find using this.