PWM voltage offset on Aux Pins

Hello guys,
anyone has experience in using PWM INPUT on Aux5 for a Pixhawk2 Cube?

I was planning to get a PWM input with the BattMonitor_FuelLevel_PWM, but…

after setting BATT3_MONITOR=12 (FuelLevelPWM) BATT3_CURR_PIN=54 (AUX5), SERVO13_FUNCTION=-1 (GPIO) and wire my external PWM signal to the physical pin, I get an Offset in the PWM at that pin when I probe with a scope.

I mean that the PWM wave “low” is 2.3V and “high” is 3v3. The original PWM is clean and swinging between 0V and 3v3, then when I plug the jumper wire to Aux5 its reference gets offset, if I unplug it I get the good swinging signal back. Ground of the probe is the same rail as the servo, of course…

I have seen this behaviour in my experience when connecting 2 push-pull pins to each other, however I would expect the Aux5 to be configured as INPUT when using the parameters I set. Anything I’m missing?

Did you have any solution?