Broken suspend on Acer Chromebook Tab 10 (google-dru)

Acer Chromebook Tab 10 (google-dru) running on edge built from pmbootstrap, with the XFCE environment (but a similar issue was observed in other environments), launched from SD card.

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I'm trying to suspend the device (for example with sudo zzz), but it stays active and doesn't enter suspension. Monitoring dmesg -w via ssh reveals this error (full log: https://gitlab.com/-/snippets/2580624):

[  554.686333] panfrost ff9a0000.gpu: PM: dpm_run_callback(): pm_runtime_force_suspend+0x0/0x134 returns -16
[  554.686357] panfrost ff9a0000.gpu: PM: failed to suspend: error -16
[  554.755705] PM: Some devices failed to suspend, or early wake event detected

Blacklisting the panfrost module in /etc/modprobe.d/ and restarting will then successfully shutdown the device when trying to suspend. But:

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Following the workaround above and suspending the device, it shuts down and immediately enters the builtin recovery menu (since pmOS is running from SD card and did not replace ChromeOS located in eMMC, you boot from SD card by selecting the option at startup). At this point you would normally either turn off the device, launch from internal storage or external storage with the power and volume buttons, but input won't then respond anymore, not even just turning the device with a short press of the power button. Holding an apparently random combination of the power and volume buttons to turn it off and repeating that 1-3 times will return the recovery menu to normal operation.

Now, if I boot into pmOS, I don't return to the state prior to the suspend, as if I just powered off the tablet.