Wifi uses interrupts to maintain your connection (either in STA or AP mode or both) While you are in an interrupt, interrupts are disabled. This is probably the reason for the abnormal behavior. But i may as well mention this now, FastLED.show() turns off interrupts while it is sending the signal to the LED-strip, timing is crucial for that. I have heard that for ESP's FastLed also has a DMA mode (as Makuna/NeoPixelBus does), but i am not sure how set that or if it uses that by default on an ESP. And this :FastLED.delay(50);Is one of the dumbest ideas i have ever seen. Rather than using delay(), which on an ESP at least calls yield() until the time has elapsed, FastLED.delay() basically calls .show until then, sending the same info over and over to chips that have that info already and really don't need to be refreshed with the same data again. Of course really you should use millis() for timing, but if you are going to use delay(), use delay() !