XPS

[StanislavTurza]

steps to reproduce

1. mute volume

2. sleep laptop

3. resume from sleep

4. no sound in any application,  mute/unmute, change volume have no effect there is no sound from internal speakers till i restart notebook

windows 10 (latest updates), all updates from dell applied 

[StanislavTurza]

as i said i have to mute sound before entering "sleep" .. after waking up there is no sound even when i unumte/change volume, again, device device is fully updated, realtek audio driver version 6.0.1.8432 (chceked)

its apparently driver issue and easily reproducable for devs

[Saltgrass]

An important setting for your system is when the Display turns off.  That is when it goes into Modern Standby.  This is a low power mode where only certain processes can happen.  The system can also continue into hibernation depending on your settings, but the sleep option doesn't mean anything.  The power button puts it into modern (connected/disconnected) standby.

This should not effect your sound, but if it is having some type of driver problem when coming out of low power mode, it might.

You could try starting Groove music and play some songs.  When the display turns off does it continue to play?  If you hit the space bar to bring the display back, does it continue to play?

It looks like that system only has one Realtek driver to install, 6.0.1.8432 which should also install the Waves utility. It is dated Aug 2018 so you might check if you have the latest one.

[StanislavTurza]

by hitting power button (power button action is set to sleep)

there are no disabled startup tasks

from event log 

12:50 The system is entering sleep. Sleep Reason: Hibernate from Sleep - Fixed Timeout

12:50 The system is exiting connected standby Reason: Transition to System Sleep State S4/S5

4:30 There is like 5 events named Kernel Boot, none of them marked as error

[Saltgrass]

Since the system is not designed to sleep, how are you putting it to sleep?

You might check the Task Manager Startup tab and see if any sound utilities and not allowed to start.

Messages in Event Viewer around the time the system goes into or comes out of whatever status it is in?