The ESP32 has two ADCs. One of them, ADC2, is actively used by the WiFi.

From the IDF documentation:

> Since the ADC2 module is also used by the Wi-Fi, only one of them could get the preemption when using together, which means the adc2_get_raw() may get blocked until Wi-Fi stops, and vice versa.

That means you can't use the ADC on any of the ADC2 channels while WiFi is on: GPIO4, GPIO0, GPIO2, GPIO15, GPIO13, GPIO12, GPIO14, GPIO27, GPIO25 and GPIO26.

But you can use ADC1, which uses pins GPIO36, GPIO37, GPIO38, GPIO39, GPIO32, GPIO33, GPIO34 and GPIO35.