Focused window bleed onto second monitor

if you pull them apart you cant cross from one window to the other....

Lending support to the idea that this is a bug with Windows.

Here's my setup:

The bleeding happens from the top of monitor 2 onto monitor 3, but not in the way I think any one of us would expect.

All monitors are running their respective recommended resolutions, with no scaling applied anywhere. All three monitors are running off the same GPU.

This is maximizing a window on monitor 2 and having artifacts of it bleeding on to the bottom of monitor 3.

Firstly, it is not just the top-most pixels bleeding over to the other monitor:

Here, you can see that it's the LOWER part of the tab in Firefox that bleeds over by looking at the Blue and Yellow colors of the squares, or the bottom of the Google or Firefox logos. This would seem to indicate that this is not an over-scan issue, or other display-related issue, because a select strip, partially down the screen on the 2nd monitor is duplicated up to the 3rd monitor.

Secondly, it depends on HOW the window was maximized.

This is the result of "bumping" the border between the monitors at roughly the center of the lower monitor:

This is the result of "bumping" the border between the monitors, on the left 25% mark:

You can see how the artifact that's generated along the bottom of the 3rd monitor can be controlled based on where I drag the window from (vertically) and where I bump it on the screen horizontally. Note the subtle differences between the height of the blue and yellow squares and how much text you can start to see in the three examples above. Note the difference in horizontal position of the highlighted browser tab in the lower two examples.

What seems to be happening is that, after "bumping" the top of the screen, it generates an artifact related to what was on the 3rd monitor when the maximize happened.

Finally,

If I hit "Maximize" on the window instead of using the "bump" gesture, I get a white line across the bottom of the 3rd monitor. Which seems to be the same kind of white bar that the OP shows along the vertical border between their monitors.

This seems to indicate that, during the maximization process, the code that handles the maximization of the window neglects to properly clean up portions of the window that were off-screen during the maximization process, for whichever screen a window is being maximized on.

Since I can control what the bleeding looks like, I do not believe this is in any way related to an issue with the displays themselves.

Try change screen resolution and see if it makes any difference?

How about if you are using other browser like Microsoft Edge, does this problem reproduces?

I have the same issue with laptop 1920x1280 100% scaling and monitor positioned on top of it (1920x1280, 100% scaling). It happens for example with Chrome. The issue started to happen after Windows 20H2 update. This is how it looks with Edge (notice the white bar above grey title bar, this is the overlap):

I cannot fix it by moving monitors further apart in display settings, because they always attach in this default position. I have updated and reinstalled GPU drivers, nothing changed. It is most probably is a bug in Windows 20H2.

I am having the same issue, unfortunately as my monitors are set up as 1 on top of 3 instead of 2x2, windows simply snaps the top monitor back to the bottom center monitor when i attempt to move it upwards. If I realign the right or left monitor slightly upwards, I can then raise the center upper monitor, but then the pointer gets stuck between the two monitors (I have to move it at maximum speed to make it hop into the other monitor between mouse polls—very difficult with a polling rate of 1000!)