Mouse scroll only works within the window frame, if you try it outside, it is broken. This is a huge problem for many people's workflow, most Photoshop tools are affected ( I also think other Adobe Programs ). The clone stamp tool with clone source is nearly unusable...
I have found the culprit and a temporarily solution: In Windows 10 go to Settings -> Devices -> Mouse -> Turn off "Scroll inactive windows when I hover over them"
If you disable this Windows 10 feature everything works as it should be!
I think all Windows 10 users are affected by this bug because the feature "Scroll inactive windows when I hover over them" is turned on by default and nobody knows about this temporarily fix. I hope you can cooperate with Microsoft to fix this issue as fast as possible.