Sometimes after sleep the monitor is only showing a quarter of screen

This is intermittent, and has only started in the last few weeks.

If the PC is woken from sleep sometimes the monitor briefly shows the top-left quarter of the image, then after a second or two blinks and shows it all correctly. The graphics is via the Intel HD Graphics 4600 with up-to-date drivers, the monitor is a Dell U2713H. PC is on 1909.



It doesn't do it every time, but to get the pic I simply pressed 'sleep', waited a few seconds and then wiggled the mouse. The part of the desktop shown is the correct size and scaling, just missing the other three quarters... It always sorts itself out within a few seconds.

Any ideas welcome.

Edited to add that the part-image is actually 40% of the total horizontal width, and perhaps just over 50% of the total height it should be. The full image is 2560x1440.

- - - Updated - - -

Updated after some experimentation...

I had Firefox open with tenforums, maximised.
I pressed the sleep button, let it settle then wiggled the mouse, and I got this:


Note in the above the top right corner where it says 'open menu', the cursor must have been on the options menu in Firefox when I pressed sleep. But on this screen the cursor is shown in the middle. It shows all the desktop this time, but if the desktop is the only thing showing then it only shows a quarter of that.

The after a second or two it changed to this, the correct display:



Very odd.