Check whether USB events might be causing the wakeup

If EHC1, EHC1 or XHC (USB3) are shown as enabled, then it's possible that a USB device might be the culprit :

grep enabled /proc/acpi/wakeup

#PXSX	  S4	*enabled   pci:0000:03:00.0
#EHC1	  S4	*enabled   pci:0000:00:1d.0
#EHC2	  S4	*enabled   pci:0000:00:1a.0
#XHC	  S4	*enabled   pci:0000:00:14.0
#PWRB	  S3	*enabled   platform:PNP0C0C:00

One can disable specific device-types using the following script :

# parse wakeup and disable wakeup for ARPT(wifi) and XHC1(usb)
cat /proc/acpi/wakeup | tail -n +2 | awk ‘{print $1,$3}’ | while read ss st;
do
  if [ $ss = “ARPT” ] || [ $ss = “XHC1” ]; then
    if [ $st = “*enabled” ]; then
      echo $ss > /proc/acpi/wakeup
    fi
  fi

However, this is a blunt tool if a single USB device is causing the problem.

Track down the mouse...

First, get an idea of which strings/devices you should be searching for :

cat /sys/bus/usb/devices/*/product

Now, specify that you need the 'mouse' device id:

grep -i  "mouse" /sys/bus/usb/devices/*/product
#/sys/bus/usb/devices/3-12/product:2.4G Keyboard Mouse

Use the device id found to disable the power wakeup (just once) :

echo "disabled" > /sys/bus/usb/devices/3-12/power/wakeup

Test the resume-from-suspend cycle is no longer triggered by the mouse...

Make the change permanent...

Shout-out : The following comes from reading all the advice on this page.

Put the one-liner above in a (probably new) file /etc/rc.d/rc.local with a bash invocation :

#!/bin/bash
echo "disabled" > /sys/bus/usb/devices/3-12/power/wakeup

And then make it executable, and usable by systemd :

chmod +x /etc/rc.d/rc.local
restorecon -v /etc/rc.d/rc.local
systemctl enable rc-local.service
systemctl start rc-local.service

Check that the rc-local.service does exist (though it appears to be defined internally, rather than through a .service file like many other services) :

systemctl status rc-local.service

All done.