Yesterday I have updated the firmware after being prompted, but after the update completed and I have restarted the Phantom 4 there was no video feed as shown in the attached screenshot. I tried to roll back (downgrade) the firmware to a previous version through the Go4 app and also through Assistant 2 (PC) - both unsuccessful. The firmware update through the Assistant downloads the firmware and fails when tries to send it to the Phantom 4. (See photos). Any suggestions would be welcome.

PS: tried the DJI Go 4 app with N-Vidia K1 tablet and Samsung Galaxy S10 - same results with both. Today I decided to spend some more time following several times the instructions from DJI support - no luck.
The only new thing I have noticed is this FOS warning.

this FOS warning also appeared...