So you minimised Recuva and and it minimises into an icon on task bar. Later when you try to maximize it, it doesn't. You can see the icon on the taskbar but there is no menu selection to maximise. Alt+tab also does not bring it up. The same thing happend to me after it searched 11 hours and showed all the recoverable files. I solved it by the following method on windows 10:
1. ctl+alt+del
2. select task manager
3. select process tab
4. scroll down and click on recuva running application
5. click on the small arrow to its left to expand the selection or right click and select expand.
6. recuva program shows up below.
7. right click on it and it shows you a menu where there is maximise option.
8. choose maximise.
