Since long time my personal workstations and laptops suspended the mouse cursor after 3-5 seconds. To use a mouse again one of the mouse buttons had to be pressed. It was particulary annoying if working for a longer time with the keyboard then needed to use the mouse. This behaviour was not WM or DE specific, it has been observed on different distributions. The reason for this behaviour was that a particular package called laptop-mode-tools has been disabling the usbhid per default. The default setting caused the mouse to suspend.

To prevent sleeping usb mouse following entry has to added in the file /etc/laptop-mode/conf.d/runtime-pm.conf

AUTOSUSPEND_RUNTIME_DEVTYPE_BLACKLIST="usbhid"

Or if having a specific DEVID it can be added like

AUTOSUSPEND_RUNTIME_DEVID_BLACKLIST="046d:c025 0123:abcd"

Then the service needs to be restarted

/etc/init.d/laptop_mode restart

Finally pull and plug in the USB mouse and from now on the mouse should not be suspended.