I’ve noticed a couple of times that when Skully (Neopixel string + Plasma stick) running the supplied code is left on for a reasonable length of time (~10 hours), the colour drifts to red with some occasional flickering. Power off for about a minute, then power on again and it goes back to the green/orange cycle (short power cycle doesn’t fix things).
I’ve checked the temp of the LEDs in the bottle; they’re peaking at about 23C. The plasma stick doesn’t seem unduly warm (and a minute off wouldn’t cool things that much) so I think thermal issues are off the table. The connections all seem sound and I think I can dismiss a wire break as a root cause (famous last words!).
Timing, perhaps? I’ve not looked at the code yet (nor have I put an analyser onto the bus), but my current guess is that the Pico may be drifting out-of-spec for the LED comms.