I had another resume failure today.
I had been using the laptop on battery for a short while–maybe 20 minutes. Then I suspended it and plugged it in. A bit later, I unplugged it, then plugged it in again. Then I came back about 15 minutes later and found the laptop was warm. I checked the power draw at the wall: 16.3 +/- 0.3 W. The laptop was unable to resume.
Normal suspend-to-idle power draw, when the battery is charged, seems to be 1.3 +/- 0.3 W.
Suspecting the failure had something to do with unplugging and replugging power, I did about 5 unplug/replug cycles while the laptop was suspended. This did induce another failure. Unfortunately, I was not able to repeat this again on two more attempts, so either the failure was a coincidence or I have not yet found the right conditions.
Both failures today were after suspending via systemctl suspend (nothing to do with the s2ram utility).
-Corey