Popup window out of view

When moving one of the popup windows it can slide up out of the viewport. Once that happens, there doesn't appear any way to get it back. Clearing the cache, clearing browser cache and cookies, nothing helps. It stays in the new off-screen position.

How can I get the window back inside the viewport?

Got it! Deleting the core/cache/ folder did the trick.

Have a look at this thread, too:
https://forums.modx.com/thread/95785/migxdb-question---or-just-a-windows-one-how-to-move-modal-window