GPIO25 as PWM output connected to GPIO33 as ADC input - voltage drop on pulse

[MarcRoma]

I am a bit stuck on this one and would appreciate help or tips from the community here...

I am using ESP-IDF and using a dev board from TTGO (with LORA).

I've programmed the GPIO 25 to have a 100KHz PWM output with 50% duty cycle.
Looking at the osciloscope I see a nice, well behaved pulse 0-3.3V, as expected.

Now, I configured the GPIO33 as ADC input (atenuation DB 11). As soon as I connected the two GPIOs I see a drop on the Voltage on the high cycle of the pulse, from +3.3V to ~900mV in the osciloscope.

I've tried different configs and always get the same result above. Am I missing something fundamental here ? Any tips or ideas ?
Happy to share the code if description above not enough/clear.

Thx for the help!