Neopixel and SD card

[Grumpy_Mike]

Is that the issue you think?

Well it is worth a shot. Does it happen with overall low light levels or does it just happen when things are bright?

This points to a poorly regulated supply or a power distribution problem. Capacitors can help with the power distribution.

Yes they are in the right place.

Is their any pattern to the misbehaving pixels? Like are they on the edge or middle of the display?

[mooop]

Does it happen with overall low light levels or does it just happen when things are bright?

It does seem to only happen with bright colors indeed.

Is their any pattern to the misbehaving pixels? Like are they on the edge or middle of the display?

I don't believe so. It's pretty random, in the center as well.

[Grumpy_Mike]

It does seem to only happen with bright colors indeed.

That seems to suggest a power supply problem.

In might be thermal, does this happen when you first switch on or is it only after they have been running for some time?
Sorry I can't be more definitive.