Repeated voice service drops on Google Fi while PS data remains registered

[cameronaaron]

I’m reporting repeated cellular voice-service loss observed on a Pixel running GrapheneOS. I collected a system log during the issue.

Observed behavior:

Cellular service repeatedly drops out and comes back.
The status cycles between normal service and “No service”
This happens many times over hours, not just at boot.
What I found in the log:

Repeated service-state flapping from roughly 07:36 to 11:55.
About 77 in-service transitions and 81 out-of-service transitions in that window.
In many events, packet-switched data stays registered on WWAN NR and IWLAN while circuit-switched voice registration becomes NOT_REG_OR_SEARCHING.
The log repeatedly shows carrier voice registration moving out of service while data remains available.
I did not find clear evidence of a full modem crash, SSR, ramdump, radio daemon death, or thermal shutdown.
I did see a small number of SIM_IO error events and some telephony / subscription refresh oddities around the same period.
Why I’m filing this:

I’m not sure whether this is GrapheneOS, carrier provisioning, eSIM handling, IMS / VoNR interaction, or carrier behavior.
I’m filing because the device is clearly losing voice service repeatedly, and I want to know whether this matches a telephony issue.
Relevant environment:

Device appears in the log as google/mustang/mustang
Build shown in the log: BP4A.260205.001/2026030701
Carrier affected: All
Network seen during service periods: T-Mobile NR, including band 71
Wi-Fi / IWLAN is present in the service-state logs
If useful, I can provide:

Full system log
Exact timestamps for transitions
Whether the issue reproduces with Wi-Fi calling enabled or disabled
Whether it occurs on stock OS as a comparison test

[cameronaaron]

This issue seems to only happen on GoS not stock