After updating a server to 20w17a from version 20w16a there are chunk glitches that you can see on maps. These chunk glitches seem to cause rain to be blocked. Or rain to go through blocks underground.
This only occurs when updating worlds from 20w16a to 20w17a and can be replicated in singleplayer and multiplayer servers
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Visual of the glitched rain on a superflat world with jungle biome.
Glitched rain appears only in chunks that were loaded in 20w16a or earlier, any new generated terrain does not have the issue. Glitched chunks on the map do not appear to have anything wrong with them aside from the glitched rain and visuals on the map.