Additional hypothesis:
The frequency seems to fit into a different (the fourth) wifi channel while the dev board is in the . Is it possible, that the ESP32 antenna calibration software automatically recognises that our antenna has a resonant frequency that better suits a different wifi channel and ...

My apologies, the picture is outdated. As I indicated we used several values for the oscillator capacitor. The theoretical best value is 16pF but we settled on 13pF through experimenting with the oscillator. The behaviour did not change and the problem persisted regardless.

My friend and I are developing a custom board for BT/Wifi using the ESP32C3 and an onboard antenna based off: [TI 2.4 GHz Antenna][/https://www.ti.com/lit/an/swra117d/swra117d.pdf].
In our first version, the BT/Wifi was not working properly. We used the tx test tone in the [ESP Certification and ...