SSMS Dialog Box issue

Using SSMS 21.5.14, but I know this issue has existed in previous versions of SSMS.

When opening a View in Design mode in SSMS, if the View contains a UNION, SSMS pops up a dialog box like the one below.   The dialog box immediately hides behind the active SSMS window and sometimes you are not even aware that it has appeared.  If I do notice it immediately, I am not able to click the OK button to clear it.

This dialog box sits happily in the background and I can still move around the SSMS interface, however it does some odd things like ignoring certain keypresses when editing stored procedures or trying to make changes in a Query window.

The only option is to exit SSMS completely and start again.  When I do exit SSMS, I get the following message:

Has anyone else experienced this and is there a way to prevent it happening?

TIA!