i am seeing this issue again today. screen goes dark / turns off after only 5 seconds. double tap turns screen on again but it goes back to where i left off and not the lock sceeen.

edit: found that this is only triggered if phone is set to silent mode.

edit2: correction.
1. if i set the phone to audible mode, problem disappears.
2. if i set the phone to silent mode, problem reappears
3. after about 30minutes, i tried setting phone to silent mode again and problem didn't reoccur.

i'll try to find a way to reproduce it consistently.