Windows 10 added a feature to use a numeric keypad to control your mouse.
If this is on, the keypad won't work properly.
To fix the issue:
Open the 'Ease of Access' settings by pressing the Windows logo key + U on the keyboard.
On the 'Ease of Access' settings screen, scroll down and select 'Mouse' in the left-hand column.
On the right side of screen, click the On/Off toggle switch under 'Control your mouse with a keypad' to turn it off.
This issue applies to either the USB or Bluetooth keypad.