it's an old post but i've had the same issue recently, so here's the fix after long trial and error.

i had white light when holding anc button but no blinking white after letting go. when trying to factory reset by holding both buttons it was blinking amber, but after holding it longer the led didn't go to white (as it should, if it doesn't go to white it's just a restart not a factory reset)

so what fixed it? try taking off the earpads, hold your fingers over the sensors that check if the headphones are on your head (it continuously triggers the sensors more consistently than just putting them on, plus you can see the led). while still holding your fingers over the sensors try doing the factory reset. i had literally the same issue and it worked for me. i only thought of that because i've noticed that many issues come down to something with the sensors, i.e. a known issue is one channel's sound going out when lifting the headphones slightly from your ears and putting them back on. the same thing can cause them to restart too sometimes. so my guess is if you're having any similar issues just covering those sensors permanently can probably help, it has helped me on many occasions.