I am not sure that this is a problem in single player but on 3rd party servers in the latest snapshots (20w17a+) Maps are broken. They have patterns of grey and black patches through them and it is hard to recognize anything on them. Also since 20w17a there has been a problem with rain. Rain goes through random blocks and on some blocks during a storm there will not be rain. This can be bad during a thunderstorm where if lightning strikes a primarily wooden build it could very easily get burnt down with no rain to extinguish the fire. These seem to be the only bugs I have found and again they only seem to be happening on 3rd party servers.
MC-182939
Rain patches and Distorted Maps (on 3rd Party Servers)
Resolved
Duplicate
0
Lukas Raynor
(Unassigned)
Unconfirmed
(Unassigned)
20w19a
Retrieved
Hello there!
The server owner needs to optimise the world. This bug was fixed in 20w18a, however it requires the world to be optimised to patch it.
I did this myself by copying the world folder and putting it in my singleplayer worlds folder, and then optimised it, and then put it back on the server.
^Sharpy.