Safe Mode, DPF (FAP) removal and ECU remapping problems

Hi
I have a G4 Grand Picasso 1.6HDi of 2006.
My problem is that after driving 30-50 Km the car switches to safe mode and will only have up to 2.800 r/min.
When I close the engine and turn it back on, everything is back to normal, but it can happen again after the next 30-50 Km.
I have noticed that the problem is most common in long upward slopes, there is no connection to whether it s winter or summer, and when it happens there is no change in engines temperature(I follow the situation through torque pro).
For the past two years my car has no DPF and catalyst and there s remapping in ECU program.
I took the car to Citroen garage and was told that Lexia cannot find any detected faults. I took it to garage when the car was in safe mode and was told they cannot find anything wrong, they believe the problem was to do with the remapping that was done , and that the original ECU program and the original DPF have to be install. Only After that is done will they search for the cause.
the problem stared 1 year after the dpf was removed and the ECU remapped.
Has the same problem happened to anyone?
Any idea of what's going on?

Thanks