So the problem always stays with cylinder 3 with injector 3 located on another cylinder ?

You need to verify signal to the injector is same as all others ( it would be very bizarre if it was different though )
Pulse width ideally so will need a suitable meter.

Another odd test....

Swap the leads between 1/4 and 2/3. As wasted spark this should have no impact on how the car runs, but if the ecu is doing something strange when it believes it is firing spark on cylinder 3, this behaviour should now occur on cylinder 2

Or if no multimeter for injector test, swap the injector plug between a pair of cylinders and see if the problem moves.

If it is still all on cylinder 3, then there is likely a mechanical issue with the engine.