Today I decided to update my Wifi v2.7.5 to the most recent one via the web interface. The upload went successful (I only pressed the upload button once, as there already seemed to have been issues by people pressing it twice), didn't get any error message or whatsoever, but unfortunately I'm stuck now with a dead wifi module. Rebooting (either via the display or by taking the mains off) doesn't have any effect either.
I guess doing a manual flash (or buying a new wifi module) is the only thing I can do to get it back to work. I do have some experience in flashing Sonoff devices and as fas as I understood I can use the same USB flash device for that, correct (in full it is a 'FT232RL FTDI USB to TTL Serial Adapter Module')?
Also, does the latest Wifi firmware work with controller firmware 4.8.5?
4.8.0 is the minimum for WiFi so you should be okay with 4.8.5.