rkeenan I'm not sure what good flashing the Google stock Pixel OS will do, but I can try.
To be clear, flashing back to Google's OS might or might not do anything.
If the Google stock OS works much better, then maybe file an issue on the GrapheneOS issue tracker.
If the Google stock OS does not work much better, then (a) GrapheneOS is "off the hook", but (b) there is a fair chance that thesome hardware is broken.
rkeenan Everything worked fine up until a few months ago. I must have did something to the device that did something to make it function the way it is functioning now, but I can't think of what.
Unfortunately, as enough time elapses, pretty much any piece of hardware will break. Sometimes broken hardware makes this very clear by making a loud noise and shooting fire out of one side, but sometimes the symptoms are more subtle.
Again, the least-disruptive thing to try next is replacing the SIM card. In a mathematical universe, because you tried that SIM card in an iPhone it must be fine. But hardware doesn't work that way. Sometimes a bad SIM card makes this very clear by making a loud noise and shooting fire out of one side, but sometimes the symptoms are more subtle.
If what's going on is a hardware problem, then that means that some piece of hardware does not behave in a way that it makes sense to reason about (e.g., "If a SIM card works in one phone then it should work in another" -- that is true for non-broken SIM cards, but not for broken SIM cards).