TLDR; Under little load the GPIO 22 reaches 3,5v whereas under more load it only reaches ~2,4V, which is not enough to trigger the reset-line on an ATMEGA328P. UART GPIO Pins still reach 3,3V in both cases.
I use the Raspberry Pi as an IOT Sensor with an Arduino(-ish) that controls the power supply (specifically the board I use is the SleepyPi 2).
I also use the Raspberry Pi to update the code on the SleepyPi.
The code I use to do this is detailed here, although I am pretty sure it is not a code related problem: https://github.com/zagatta-sonah/KeePiLive
To flash the SleepyPi (ATMEGA328P) I have to pulldown the GPIO 22 from 3,5V to trigger the reset line for the bootloader to accept my code on the UART bus of the Raspberry Pi.
Notice the green line that goes from 3,3 to 0V.
When I run the same code within a the larger Architecture of the my IOT Sensor (which obviously does a lot of other stuff), the GPIO unfortunately does not reach 3,3V but just 2,4V so the reset line doesn't trigger and I can't flash.
Notice the green line only reaching 2,4V. Also the GPIO pins for the UART bus still reach 3,3V.
Any ideas on how to solve this?