Hi, trailing edge calibration is correct for LEDs, but have you done/checked the following already
- Dimmer2 current in the App - what current at 100% and when the lights get darker?
This would give you some important information!
Otherwise:
- complete factory reset
- no scenes running that will change brightness or switch to night mode
- is anything else running in this room or on this circuit, which overloads?
- check if you have a break somewhere in the neutral line?
- replace d2 with a shelly1 or another dimmer if you have one to check function
Peter