I ran into this too - it had to do with working remotely and remotely connecting to a computer (even thought my monitors at work and at home are the same size, somehow the system settings didn't match).  I think the trick I came up with was to cascade the items.  Another trick was to go to Task Manager and double click on the item from there and it brought it up, I think.  I'm sorry I can't completely remember as it happened at the beginning of COVID when I was working from home... hope this helps a little and someone else can chime in with more details.

Siri is right about the cause. This is what I do to fix it. While holding the SHIFT key down, right-click on the application in the taskbar and then click Move. Hit the right or left arrow key a couple of times and then use the mouse to pull the window back into view. This usually works.

It also happens on my desktop computer - not just when I remote in

Yes, it did to me too - but I was told that was the reason why, because of the remoting in from elsewhere.  I think the only time I had the issue was when I was back in the office.

There is also an issue if you are opening Sage Desktop on your office computer on a monitor other than your primary.  Then Task, Report, and other windows opened directly from Desktop seem to open behind Desktop and cannot be accessed.  To resolve this issue (if this is what is happening on your system) is to move Desktop to your primary monitor, close it and reopen it.  Then never move it from your primary monitor.

You should then be able to open windows from Desktop or from within the application and always be able to access them.  Your application windows, or any windows opened from within Desktop can be placed on other monitors as long as Desktop remains on your primary.