I have 3 Pow. Two updated fine. One is always stuck at 90%.
Overall I am seeing just below a 30% failure rate across Sonoff devices. Their tech support wasted loads of my time suggesting pointless things and now hasn’t replied in over a month. Essentially there is no warranty on their products.
Don’t do anything they say unless they can explain a logical explanation why. I think they just have a long list which they copy and paste without thinking.