Problem in games. When fps drops below 60, everything lags and freezes. What to do?

Question

Windows

When playing above 60 fps, everything is fine, but when the game drops below 60 fps, it starts to lag and freeze. That is, even one frame will fall - 59, it starts to gouge out ... Although in fact this should not be, only if it falls below 30 ...
In general, the monitor is 60 Hz, but overclocked to 75, when changing back to 60, in games are the same. So everywhere, in any game where it sags below 60 fps.
Configuration i5-7400, 1050 Ti, 16gb, 500w.
Cable to displayport monitor. Firewood is the latest, dx 11-12 is also all the latest, there is no difference. Disabling, enabling vertical synchronization and triple buffering does not help, when changing the frequencies of the video card it does not affect in any way.
I think that the problem is either in the dp wire or the monitor.