suspend to ram fails on new pinephone kernel >= 5.16.x (often when charger is not plugged in)

Describe your issue

What's the expected behavior?

Phone will suspend as expected.

What's the current behavior?

Over half of the time, suspend to ram fails.

How to reproduce your issue?

~$ uname -a
Linux pine64-pinephone 5.17.0-rc8 #1-postmarketos-allwinner SMP PREEMPT Mon Mar 21 08:33:05 UTC 20 aarch64 GNU/Linux
~$ doas rtcwake -m mem -s 60
doas (user@pine64-pinephone) password: 
rtcwake: assuming RTC uses UTC ...
rtcwake: wakeup from "mem" using /dev/rtc0 at Mon Mar 28 11:23:45 2022
rtcwake: write error

using other parameters for -m shows that the timer is set, but the suspending to ram fails.

What device are you using?

pine64-pinephone

On what postmarketOS version did you encounter the issue?

• edge (master branch)
• v21.12

On what environment did you encounter the issue?

Phone environments

• Phosh
• Plasma Mobile
• Sxmo (Wayland/Sway)

Other

• No environment
• GNOME
• KDE Plasma
• Kodi
• MATE
• Shelli
• Sway
• Weston
• Xfce4
• fbkeyboard
• i3wm
• Sxmo (Xorg/Dwm)

How did you get postmarketOS image?

• from https://images.postmarketos.org
• I built it using pmbootstrap
• It was preinstalled on my device

What's the build date of the image? (in yyyy-mm-dd format)

Additional information

I think previously, it would suspend not to ram when suspend to ram failed? Or at least maybe the wakeup would require a boot instead of resume..

~$ echo $SXMO_DEVICE_NAME
pinephone-1.2pine64

Based on comments below, this seems strongly correlated with the charge state.