Not a game-breaker. And I've only tested this in 1.15. As far as I can tell from searching, no one else has reported this, either.

I have an AFK fish farm on a singleplayer/LAN world. (That works either way) And whenever I catch a fish, The rain comes through and is rendered in the building. As I'm creating this post, we also figured out that it's not an issue with fishing, it is triggered by a player collecting XP. My sister is connected via LAN and as I attempted to capture footage of the bug, she was triggering the glitch on my screen by collecting XP after killing a zombie.

Again, not a big deal in the gameplay sense, just thought it should be brought to attention.