Ubuntu 18.04.2 immediately wakes up from suspend

I had the very same problem after upgrading from ubuntu 16.04 to ubuntu 18.04.

I solved by disabling the wakeup option for the device that in my case was enabled.

$ cat /sys/bus/usb/devices/*/power/wakeup
disabled
enabled
disabled
disabled

$ ll /sys/bus/usb/devices/*/power/wakeup
-rw-r--r-- 1 root root 4,0K mag 19 11:04 /sys/bus/usb/devices/1-7/power/wakeup
-rw-r--r-- 1 root root 4,0K mag 19 11:02 /sys/bus/usb/devices/1-9/power/wakeup <-- the bad guy
-rw-r--r-- 1 root root 4,0K mag 19 10:46 /sys/bus/usb/devices/usb1/power/wakeup
-rw-r--r-- 1 root root 4,0K mag 19 10:46 /sys/bus/usb/devices/usb2/power/wakeup

But what really helped me to identify the device were its ids.

cat /sys/bus/usb/devices/1-9/idVendor
8087
cat /sys/bus/usb/devices/1-9/idProduct
0a2b

After googling a bit, turns out it's the bluethooth controller.. https://usb-ids.gowdy.us/read/UD/8087/0a2b

Finally disable it

echo "disabled" >  /sys/bus/usb/devices/1-9/power/wakeup

Now my laptop really suspends. Hope this helps you too.