Did you build in any detection/reset for wifi hardware issues? I'm jaded and assume this will be a thing with everything prior to the rpi4. (Mostly my experience here is specifically the rpi3b)
Haven't built any detection in so far, but if I do notice instability, then taking a look at kernel logs should reveal those pretty well with USB device reset messages popping up.
I have never used the WiFi on newer Pi-s that shipped with it, so I cannot say how reliable that was. The USB WiFi adapter seems to work quite well, assuming you have the firmware packages present (included out of the box on Raspberry Pi OS).
Of course, could be the USB wifi more reliable.