I’ve had a very similar issue with my Octavia 4 facelift (13" infotainment). The screen started flickering about a month after I got the car. I went through multiple checks and even had the wiring harness replaced, but the problem persisted. According to a TPI (TP 2077768/2), the issue might be fixed with a future software update, though there’s no clear release date. On July 1st, (after many complaints and emails to Skoda Czech Republic, the local importer and the local car dealership) the dealer replaced the media unit, but I’m still skeptical that this has really solved anything because the unit sometimes powers on by itself when I open any door or the tailgate. I'm still monitoring the behavior of the infotainment system.