P: Scrolling images in Loupe view doesn't work

After installing the 2015.4 update today, I can no longer scroll through images in Loupe view with the mouse. Keyboard scrolling via arrows works, mouse does not, to go from one image to another.

Scrolling in the Grid view works fine. I tried two different mouses to make sure.

This has never happened in any of the previous versions on the same computer.

Any ideas?

Thanks