JJ1992 I'm going to repeat what I've said other times in this thread, to my knowledge GrapheneOS hasn't modified any of the related code so it's very, very unlikely that the issue you're experiencing is caused by GrapheneOS. It's most likely caused by a bug in AOSP or by the carrier.
As I recall, there was some issue not long ago that Google fixed. It's possible more fixes are in QPR3, so make sure your phone is up to date.
Finally, if any of the developers could reproduce the problem, I think they'd fix it promptly if it's something they can fix.