rodent56 I fixed it. The culprit was that I denied network permission to ImsService(com.shannon.imsservice)! If this package is that important, GOS team should make it impossible to revoke its permissions like other system packages.
Regarding this System app/component (ImsService):
matchboxbananasynergy This is a completely normal app from AOSP, please don't touch it or adjust its permissions, you'll just end up breaking functionality.
Users should STOP removing permissions from System Apps/services, plain and simple. Why you might ask?
matchboxbananasynergy As a general rule, you're achieving nothing by disabling permissions from system apps. The only thing that's going to end up happening is things breaking and us not knowing how to help you fix them, since we won't know exactly what you've changed.
If you trust GrapheneOS, there's no reason to be adjusting permissions or anything else for system apps.
And
GrapheneOS It's fine to change permissions for the bundled user-facing apps but you shouldn't disable or mess with the permissions of OS components.
Also
treequell you should not disable or change the permissions of any system apps. I can understand the temptation to do so, but it will likely break things. The Settings app, specifically, is a privileged app and an integral part of the OS. As you're trusting the OS by installing it, you'd be best off leaving those permissions to their defaults.