Random blackouts on 10-year-old A1407 Thunderbolt Display

Recent versions of macOS are reportedly pickier about display transmission errors – as in, they don't want to see any, and will cut resolution or cut the signal if they do.

The cable might have been flaky all along, and the macOS upgrade might just be making that more apparent.

Could be a bad all in one cable. Try a TB2 cable connected directly to one of the TB ports on the display bypassing the built in cable.

Is this happening since the oS update? I updated my 2018 Mac mini with two 1407 Apple monitors on it and found out that there's apparently some sort of glitch causing just the one monitor not to turn on. I switched them around, tried different ports and even tried to plug it into a laptop and still nothing. Rolled back the OS and it works just fine. Called Apple prior to reinstalling the OS, and they insisted that it was a bad monitor. I guess all I'm suggesting is that if it started doing it after the update, that it could be update related.

I encountered this type of issues on 1/3 of my TB displays -- most of them were bad logic board (except 1 bad power supply).

The repair can be a challenge - even the parts can be found on line.