When mod "Weather, Storms & Tornadoes" is installed. Sometimes firebending does not work in clear weather. While the actual rainfall, et al, is prevented by Weather2, The '/weather clear' command clears whatever event is remaining.

https://www.curseforge.com/minecraft/mc-mods/weather-storms-tornadoes/

Is this still a current issue?

Huh. Ngl that's probably because it overrides the default mc rain. I'll see what I can do.