I think Mullvad VPN does detect when a device is offline, as the sticky notification in the notification drawer reflects this whenever offline (especially after a reboot).
Since my last post, I've started to pay attention to Auditor when my devices had been offline for a bit (due to either rebooting or being in airplane mode) and I noticed that Auditor checks somewhat more quickly on the Pixel 5a and Pixel Tablet. (Though my SIM card is on the Pixel 5a, so it's hard to tell with basically internet basically always being on.) Sometimes Auditor will retry in a rather short amount of time (smaller than 5-10 minutes), especially on Pixel Tablet.
Also, Auditor will recheck quickly a bit quicker than I remember, even the Pixel 4a without manual intervention (which I described above), though it seems to be a bit slower. (This is probably because Pixel 4a's SoC is overall slower than Pixel 5a or any other newer Pixel devices.) (I happen to have the Pixel 4a around, as Auditor is still supports it.)

Option to manually trigger remote attestation #197

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