Is this frame skipping or something else

[Zelectic]

Hello, i overclocked this monitor (S22B300) to 77hz a month ago and didn't do tests to see if it was a stable overclock, today i checked the frame skipping test, and got this images, so im wondering what is causing that?

I took the picture with 0 brightness on monitor and a SAMSUNG A5 2017, if that helps.

[RealNC]

That could be a camera artifact. I've seen discussed here before. IIRC, if there's no empty boxes, there's no frame skipping.

You can also look at the normal testufo framerate test. If the UFO is always moving completely smoothly over the screen, then there's no frame skipping.

[YaWutMate]

This happens to me to i have a VA panel at 144hz, however i can barley see this effect with my eyes also. i made a post about it and waiting for replies.

[Chief Blur Buster]

The first/last squares are normal (it's simply a camera rolling-shutter artifact), so I ignore first/last squares.

Contrast enhanced and zoomed, there are two brighter squares, so possible explanations:

Frame Repeating Artifact
There might be frame-repeating artifacts (this occurs when a monitor runs at a higher Hz and downclocks, e.g. emulating 75Hz via a 90Hz as an example). If this is the case, try upclocking a little further like to 90Hz or 96Hz -- just in case your monitor is somehow suddenly choosing a higher overclocked fixed refresh rate in order to do the mid-overclocks successfully. Does the monitor stay in sync when you do that?

Backlight PWM dimming flicker
If you have a PWM-dimming backlight, some refresh cycles will have more PWM pulses than others. That makes certain squares brighter than others. This is very bad when your PWM dimming becomes unsynchronized with your refresh cycles -- a common problem during display overclocking. Fixing this can be done by setting backlight to 100% brightness (and then using either F.Lux -- or NVIDIA Control Panel dimming -- or putting a ND filter/cellophane in front of your screen)

Variable refresh rate monitor with varying refreshtimes
It may also happen with variable refresh rate monitors that has unusually high variance in refresh cycle durations during fixed-Hz mode (windows desktop) though I haven't seen that before. This can happen with games (fixed average framerate with slightly erratic frametimes/refreshtimes) but buggy framepacing in overclocked windowed FreeSync may potentially create this. If you have FreeSync enabled, try temporarily disabling FreeSync and see what happens.

Camera behaviour artifact
(Only if you don't see it with your eyes) This is rarer, as a camera shutter is open for a consistent duration from start to end. However, some cameras use a series of briefly pulsed shutters to emulate a long duration shutter, and it has the same issue as a PWM dimming backlight except done at the camera-side, if a pulsed shutter occurs more times on certain refreshes than other refreshes. To be sure this is not a factor, testing with a different camera.

...Those are the explanations I can think of.