Tried using the command /weather rain, and the sky changes to overcast, but it never actually rains. I changed to thunder and received the message "Set weather to rain & thunder" but still no rain. However the thunder did appear.

/weather clear brought the weather back to clear. Setting the weather directly back to thunder made the thunder return, but no rain.

seed -8300275442758179407
xyz: 1286 69 975

Edit: It is raining the biomes next to the savanna I'm in, but it won't rain in the savanna. Adjoining biomes are beach and lukewarm ocean.