System does not resume after pm-suspend when no display/screen is connected

I have a weird issue and already spent some time googling but without any success.

I did a fresh install with 3.0.86 after my USB pen drive suddenly stopped working. I was running 3.0.x since Feb 2016. Although the previous system evolved over time and lots of beta versions, it did its job.

The fresh install is even running better except one issue: The system will only resume after standby if a screen/display is connected via HDMI. As this functionality is crucial I must find a solution to it. I don't have a screen where the NAS is being placed.

This is what happens

Alternative 1 (No screen connected)
1) System is running / no screen is connected via HDMI
2) issuing pm-suspend
3) System is in standby (S3)
4) waking up system using WOL or power button
5) In 90% of the tests, the system hangs during wakeup (PINGs are replied but nothing else works, not reaction on ssh either). In 10% of the tests the system resumes as expected
6) Once HDMI with display is plugged in, system resumes immediately as expected

Alternative 2 (Screen connected)
1) System is running / screen is connected via HDMI
2) issuing pm-suspend
3) System is in standby (S3)
4) waking up system using WOL or power button
5) system resumes immediately in 100% of the tests

So I had look into the logs which confirm my observations:

https://pastebin.com/ZinC5rrP

You can clearly see that some resume operations work fine, e.g. network and disks until a certain point in time (line 1-44). This is the action taking place before the HDMI cable and screen is connected. The system then hangs until you plug-in the cable. Once cable is plugged in, it becomes clearer what caused the issue. The call traces refer to the intel graphics driver.

However, my experience ends at this point as I don't know what exactly in the driver causes the problem or if it is another problem and the driver is just revealing it. I already updated the intel-driver from the backports repository but that did not change the situation.

Any help is much appreciated.

Thanks.

Thanks @cabrio_leo for the input. Although the links point to a different problem (omv does not boot at all without screen), it made me think about it differently and

the solution to my problem is: Internal Audio must remain enabled in UEFI. With that being set, I don't have any problem with a headless resume from standby.