Hello guys,
on my Audi TT 1.8t 225 with APX engine, I swapped the original ECU ME7.1.1 018AE to a ME7.5 018H from a 1.8t 225 BAM engine. I installed a new Bosch LSU4.2 O2 sensor, I made the necessary connections, an I added a relay to give +12v on PIN 121 when I turn on the ignition, with ground commanded by ECU pin 21, accordingly to the schematic.
On new ECU I did immo off and all necessary modification on flash to suit the engine.
When I crank the engine, the first time I turn the key the engine won't start. I release the key and I crank again and the engine just starts fine.
After start, the car run nice and smooth, I did logs and everything seems normal. The remap now is only to adjust electronics to engine's sensors and actuators, no performance modifications at all... For now.
I would like to have any advice about what should I look for, maybe someone knows what's happening here. I printed the schematic of engine's wiring from APX and BAM engine's, I checked the continuity of every conductor and connector, I checked the correct wiring for supplying the ECU, I don't find any problem. I reverted to the original ECU and it works pretty fine!

Can someone point me any direction to find the problem?
Thanks in advance, best regards.