I don’t know if it’s related, but this same issue was reported here: https://github.com/jgarff/rpi_ws281x/issues/208
And is claimed to be resolved by the suggestions here: https://github.com/jgarff/rpi_ws281x/issues/188
I’m confused that this problem has suddenly appeared out of nowhere, and that I haven’t encountered it myself, but it seems like there’s a potential fix in these issues that I will have to test this coming week.
If you’re confident tweaking the libraries and want to test this solution earlier, you could try grabbing the code from GitHub and editing this line: https://github.com/pimoroni/unicorn-hat/blob/master/library/UnicornHat/unicornhat.py#L15
…to read “LED_DMA = 10” and then reinstall the library from this source with “sudo python ./setup.py install”.