Comment 162 for bug 1566302

Same problem. However, I noticed that the issue disappears when you modify the Dell firmware settings, e.g. updating the firmware, changing settings, ...
I reproduced this solution a couple of times. Then, the problem re-appears periodically (perhaps after a kernel upgrade?).

Moreover, I suspect that this can be related to the "fastboot" feature in the firmware. In my case it is activated. Maybe, after changing the firmware, the system performs a full boot procedure, correcting any system issue related to suspension. In the normal boot, however, these checks are not performed, so the issue appears again and again.

Can you confirm if this option is activated also for you?
Maybe you can try to disable it and see if the suspension issue disappears.