CPU SPIKE / HIGH DRAIN / HIGH TEMP ISSUE - maybe resolved in V22
I've only been on V22 for a day, but my issue with certain apps intermittently causing CPU spike seems to have disappeared.
I had an issue where occasionally the temperature near the rocker switch would go very high. Battery drained much faster. This could go on for hours if unnoticed. Opening/unlocking and going to the desktop, and then scrolling back and forth between desktops was very jerky whenever this happened. The issue would often go away just by closing and re-opening, but I also found it disappeared as soon as I opened GSamBattery app. I noticed in GSam that CPU would spike to constantly 100% during these occurrences.
(I installed GSamBattery to try and track down what was going on, and then once I discovered it has temperature alerts, I set that up to detect whenever this strange CPU spikes occurred)
Over time I discovered that there were a couple of apps that shortly after using them, this CPU spike event would occur much more frequently. However, it didn't necessarily happen right when a particular app was just used. I could have my phone tucked in a pocked for a half hour and no problems, then suddenly the issue starts.
Since V22 I have tried using those apps to see if I could get the issue to recur, and so far it hasn't. So that's good.
POWER SAVING NOTES
I also noticed that after V22, my weechat running in tmux running in termux, would ping-time-out while the phone was closed. It never did that before V22. I guess that is the new more aggro power saving in action? I was able to resolve that by allowing tmux to hold a wakelock.
Finally, I did NOT notice much improvement in battery drain under V22. My battery was pretty much down to 15% by the end of the day, as it normally has been. NOTE that I didn't turn the wakelock on until later in the day.