After updating to Pie a few days ago tonight I had my clock move back from 00:30 to 19:30. (I noticed it because my blue light filter turned off). Phone uses automatic timezone so I toggled location on and off to ensure it wasn't that. I manually fixed the time and then set it back to auto. It reverted to the wrong time.
Restarted phone and it booted with correct time but reverted five hours back after about five minutes. I rebooted in safe mode and the bug is continuing. It flickers between the times every few minutes and settles on the incorrect early time (three times in the last five minutes)