I have tested this with several different ESP8266, bought from different vendors.
As I continue to research - I see the same issue here:
Sounds like it is being chalked up to “garbage on GPIOs 2 and 1” (my two outputs) at bootup. Is there any practical way to mitigate? I have a full setup with level shifters in place.
Overall this is not a terribly severe issue - but an annoying one.
It only presents itself as a problem if you are only running less than 13 LEDs, and have extras after that you don’t plan to use and don’t want to cut off.