Hi Dominik,
On my MP4, the pedelec does not prevent the throttle from working, but perhaps the more recent SP5 controller is slightly different to comply with legislation
(as some countries do not allow throttles to be used) in which case the pedelec may be supposed to only work on its own.
Have you tried adjusting the PAS Ratio using the Bluetooth App to see if it makes any difference?
My MP4 also has the BAC-601 LCD Display unit connected which allows the amount of assistance to be selected while riding, but my throttle still works normally regardless of the selected pedelec mode setting.
I would suggest checking the 5V supply between the Red and Black wires on the pedelec sensor while it is plugged in.
If it does not read 4.5~5V, try unplugging the connector and measuring the voltage on the pedelec connector on the motor harness.
If you get a good reading with it disconnected, but a very low reading with it connected, it might be a faulty pedelec sensor or even a short in the pedelec sensor wiring.
If you still have 4.5~5V with the sensor connected, I would expect the throttle to still operate
(unless the disabling of the throttle is an intended feature of your particular controller).
Looking at your photos, the pedelec sensor seems to be fitted correctly and the arrow on the magnet ring appears to be pointing in the correct direction.
If possible, try moving the magnet ring closer to the sensor to see if it helps, but if this is not possible
(and you are still unable to get the pedelec to work) you will have to contact your supplier and see what they can suggest.
Alan