Hi, let's see how we can help!
Could you please expand on how you installed sandboxed Play services? The recommended method of installation is installing Play Store from the "Apps" app (GrapheneOS official app repository), which also installs the required dependencies (GSF and Play services). Also, make sure Play services is exempt from battery optimization.
Google Camera & Maps work without Play services (Google Camera only requires GSF) so they might not tell you much. Have you seen a persistent notification telling you that "sandboxed Play services are running"? What happens if you go to Settings > Apps > Sandboxed Google Play? Also, have you tried installing Google Classroom after you installed Play services? Some apps may require that to make use of Play services.
If none of this worked, then you should disclose the debugging information privately to GrapheneOS developers. You can do that by using the bug capture tool in developer settings, or
adb logcat from a PC. We may give you more details if it comes to that.