Same issue here. Thumb (flat press) doesn’t work on Lock Screen and swipe down notifications screen too which looks the same. So, I think it can be patched if Apple wants to.
other info from my debugging experience:
1. Screen protector on, case off = everything works fine.
2. Screen protector and case on = thumb does not work well on lock screen
3. Screen protector on, case on, but I touch the metal part of the phone with a finger while testing the Lock Screen = everything works fine
4. Both on, use fingertips only = everything works fine