Casper V.

I also have this problem with my iron farm, my waterstream is 3 blocks wide
My temporary fix is by placing signs on the walls, so only the middle one can be used for spawning, the Iron Golem needs 2 block of space so it won't suffocate in the signs 😉

/summon minecraft:chicken X Y Z {Passengers:[{id:zombie,IsBaby:1}]}

I was actually just trying to fix the problem by Optimizing the world in 20w20b (in Edit.. menu) when I saw your comment.
I loaded it up in 20w22a with the log open and it didn't have any problems anymore 🙂

You can change it at https://my.minecraft.net/en-us/profile/

Hey Violine,

Yes I am playing in snapshot 20w17a, although this happened the whole session, today it seems to be fixed?

So yes it is fixed, but apparently not completely? 

I killed 3 patrols it gave me 3 Ominous Banners in total and they could be stacked.

It doesn't show the patterns until you place the banner, but then you can't stack that banner with the other 2 which haven't been placed. If you place these down, you can stack the 3 banners again.