Neopixel RGBWstrandtest example crashing

I'm new to this but have successfully setup a SK6812 RGBW strip with an ESP8266. Everything appears to be working correctly, and I can light the LEDs as I please. However, in the middle of the RGBWstrandtest example, the whiteOverRainbow() function fails and causes a reboot. It will then go back to the beginning, do the colorWipes fine, begin to do the whiteOverRainbow, the white travels about 10 pixels down the strip, and fail again at the same point.

Serial monitor shows a soft WDT reset, and using the debugger indicates a problem with this line:

if((millis() - lastTime) > whiteSpeed) { // Time to update head/tail?

I'm not exactly sure what the issue is, or how to debug from here. I have tried lowering the LED_COUNT thinking perhaps it was a memory issue or something along those lines, but that did not help. If I comment out the call to whiteOverRainbow(), the rest of the functionality works fine and continues to loop as it should, without reboot.

Please read the forum guide in the sticky post. We can't help much knowing so little. Post your code, schematic and links to components.

Include full details of how the circuit is powered, as this is often a cause of problems for beginners using led strips.