We had the same issue.
The reason (for us) was that Windows 10 has touchscreen enabled by default.
We were able to move the sheets around by holding our finger on the screen for a second or two and then dragging them around.
I've noticed this touchscreen issue causing other problems as well, and I once tried disabling touchscreen and it didn't fix the problem with Qlik.
So I think Qlik needs to do a better job of letting the user know if touchscreen controls are being used or not and where, since it is not consistent.