@biscuit_tosser_88 I agree that asking in the chat rooms might be helpful. There's a good chance someone there might have some suggestions we haven't thought of. But considering you've had this issue on GrapheneOS but not with the Stock OS, I think you can also open an issue in the Issue Tracker.
If you do open an issue there, you can mention this thread, but I think it's most important to highlight two facts: you don't have this issue while running the Stock OS and while running GrapheneOS only one of the SIMs is working, but never both at the same time.