S3221QS, sleep, sound problems

Hello,

I've been owning a Dell S3221QS monitor for about 8 months and I've been quite happy with its big display, vibrant colours and the deep blacks provided by the VA technology.

But, since a few days, some problems started to appear and they are very annoying:

- First was the sound problem. The sound comes from the speakers of the monitor, well, when it wants. It is correctly detected by Windows (Windows 10) and there is absolutely no problem in the settings, but sound doesn't come out. When searching for a solution I navigated through the OSD of the monitor, sound section, and noticed that when I turned the sound off in the OSD, it's impossible to turn it on again! When I choose the On option and validate it, it is accepted but stays off on the OSD. The only way to turn it on is to make a reset to factory settings, but here again, if I turn it off it's impossible to turn it on again. It has not always been like that and I clearly remember having been able to turn it off and on without any problem. By the way, even when it's on, I don't always have a sound. Sometimes the sound works, sometimes not, and it seems to be related to when the monitor goes out of sleep, which brings me to the second problem which is much more annoying

- The monitor doesn't want to come out of sleep mode. This happens when the computer has not been used for several minutes and turns the screen off. Then the monitor is in sleep mode, it's black but not totally off.

Then I decide to move the mouse or use a touch on the keyboard to wake it up, and nothing happens, the monitor doesn't wake up.

You could tell me that the problem comes from my computer BUT this is the very strange thing: the OSD is completely impossible to use! All the monitor buttons are unusable, they do nothing! The only thing I can do is to maintain the power button to turn completely off the monitor, then turn it on again but even in that situation, it doesn't wake up and the OSD still doesn't work. Very strange thing. So I still don't have found a solution, I have to turn around touching all the buttons, moving the mouse turning the monitor off and on and after a moment it accepts to wake up.
The computer is correctly working behing the black screen because I can turn on or off the caps lock on the keyboard and the light turns on and off on the keyboard. Then if the computer was the culprit, the OSD would work and that's not the case.

I tried to change several things like the fast wake up mode but it didn't change anything.

It seems that when the computer goes back from a deep sleep mode (when the fans and disks are stopped and it's like it's been turned off), the monitor wakes up correctly. The monitor only has problems after a "light" sleep (when it has been turned of because it was not used for a few minutes).

Is it a known problem?
Fortunately my monitor is still under warranty but it would be a pain to send it back for a replacement or a repair and not being able to use it for weeks.

Hope my message is clear and fully understandable since English is not my former language (I'm French).
Thanks for any help provided.