Is it just me or does is seem a little bit impossible for a solar flare to affect the rim world while obscured by the moon?
Also rethink the solar flare mechanic to not affect electronics deep under mountains or something, after all it is radiation, so scientifically could not penetrate rock at that depth.
No it isn't
A solar flare is a massive eruption of solar particle, so it is a wave.
And at school physik you should have learned that a wave newly expand after a blocking object.
(https://tse2.mm.bing.net/th?id=OIP.07-om8pe4eAwf-qdiadGdQHaEK&pid=15.1&P=0&w=304&h=172)
So a planet behind a moon still can be affected.