I'm on macOS High Sierra, all updates installed. So it seems like it is specifically the interaction between this tablet and a Mac (I have tried 3 different machines) that's problematic. I then thought that maybe my adapters were faulty, but both work perfectly when plugging a different monitor into both computers. I assumed it could be a faulty tablet or 3-in-1 cable, but when I plug it into a games console (without an adapter) the cintiq acts as a monitor just fine. I plugged it back into my old Mac with the old setup that has always worked.to find it just says 'no input signal' again. The tablet itself still works like an Intuos, but it won't work as a second monitor. This worked fine for about a week, when suddenly one day, the display stopped being recognised and now it just says 'No input signal' I got a newer Mac a couple of weeks ago, and had to buy an HDMI to USB-C adapter to connect to my new computer. So I've had a Cintiq 13HD for about 5 years, I've always connected to my Mac via HDMI to DisplayPort adapter, and it's worked fine the whole time.
