i had the same error on my octavia 4. turns out a damaged speaker (rear passenger door in my case) which was shorting out, had blown the infotainment computer as the sound is broadcast through the system speakers. so several diagnostics later and 1800 euro for a new infotainment unit its back up and running. the fault on the speaker only showed up when the new unit was fitted and it was overheating the computer. the sound system scan then showed the faulty speaker. you couldnt test the sound systems when the infotainment unit was failed looks like there may have been some water in that door at some point. i hope your fix is cheaper than mine !! hope this helps someone. seems mad that the skoda systems allow a speaker to do that