It is a common issue on an ESP. WiFi needs interrupts enabled to work properly and show() disables them for the time the signal is sent. WiFi is not compatible with a 'bit-banged' LED signal. You should switch to a library that support DMA mode on an ESP, like Makuna NeopixelBus or even FastLED. There will be restrictions on which output pin to use, but your wifi will work correctly again.