Turning monitor off/on makes a complete mess of open programs?

[mjaaay]

I use a single 57" Samsung monitor (7680x2160 125% scaling) with a couple of near identical PC's (both have 4090 cards) and all has been fine until I re-installed Win 11 (24H2) on one machine.

 

Since that new install, If I have say 8 programs/docs open all nicely arranged and resized to my liking on my big screen, once I turn my monitor off and then on again, all my neat layout has been completely wrecked with some programs shifted about the screen, resized smaller and stuff hanging off the bottom of the page which is really annoying and is becoming un-workable now with so much stuff being moved about.
Davinci resolve gets hit really badly where it completely changes the layout and any open Photoshop images open end up on the left side of the screen with massive, oversized windows (even though the actual images sit in the top left of the oversized window) yet the PS program screen itself remains on the right hand side of my screen (but hanging off the bottom of the page now).

I thought it could be a display port cable issue so have changed cables and tried HDMI instead with no change.

I even re-installed Win 11 again with just the hdmi cable plugged in and its still no different.

I've also tried a registry hack I saw but that made no difference.

If I switch sources from the monitors built in KVM (so the monitor stays on) to the other other PC and vice versa, the layout doesn't get broken.

 

Is this just a Win 11 24H2 issue as it was fine with 23H2 as I've made no change to my monitor settings?