I was randomly testing some minecraft features and I noticed my simulation distance has dropped with 1 chunk. It used to be on 12. Now it was 11. When I change it back to 12, it goes back to 11 as soon as I save it. I tested a couple more simulation distances and it is dropping on:

10 -> 9
12 -> 11
15 -> 14
16 -> 15
19 -> 18
22 -> 21
24 -> 23
25 -> 24
27 -> 26
30 -> 29