It has been happening to me during the last snapshots. It rains under any type of block. Under caves it also happens.
I leave attached images of my current configuration.
Sorry if I made a mistake in this post, it is the first time I do it.
Greetings and thank you very much for everything!
Environment
Windows 10
You probably opened your world in 20w17a, which corrupted it. See MC-179845 for details.