I've also experienced this since, if I remember well, build 2024123000. I have Pixel 8 (non-Pro). The bug might have been added before that, but I had no need to change the Battery Saver percentage schedule before starting to use the 80% limit introduced in this update. Perhaps the bug was already there, but not messing with the Battery Saver settings didn't trigger it (which would've caused it to reset to 20%).