I think I figured it out.
I had previously changed my resolution to 1920x1080 and forgot to change it back.
Being in fullscreen using a non-native resolution is probably the issue.
I tried to put the game in fullscreen on a 4k monitor (3840x2160) and it flickered a lot! More precisely, I saw 1 frame, then 3-4 frames of black, then another. I had about 2 to 4 "correct" frames per seconds for about four times more black.
I have Windows 10 64bits, an NVidia GeForce GTX 960Ti and an AOC 4k monitor (I don't remember exact model, but I guess it doesn't matter) running at 60hz.
If you need more details, I'm all about helping a fellow programmer. I speak french, if that's your primary language.