Rain patches and Distorted Maps (on 3rd Party Servers)

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.