Spreadsheets "disappear" within open Excel Window

This is a recent phenomenon: when I have several spreadsheets open in the same Excel Session I often want to look at both sheets simultaneously side by side. Very often, but not always, when I click on the "Restore" icon (which is supposed to make the current spreadsheet smaller than the whole window) the spreadsheet "disappears". The sheet remains active and I can actually see in the upper Name Box which cell is active but the spreadsheet is somehow moved offscreen. I can usually get the document visual again by closing it and then reopening it in Maximize mode so there is no real danger of losing data. This is just a major impediment to efficient working with several worksheets active and open simultaneously.

Is there a setting that I can make to solve this issue?

Thanks, Daf, that seems to be the trick. When I am on a single screen the "restored" spreadsheet seems to think the second monitor is still present. Cascade brings all to the top & left of the open window.