It took my a hours to figure out what is wrong and I finally nailed it down to:
PROBLEM 1: AC 9560 is not working in 2,4 GHz 40MHz n-mode
I don't know if this is just the case because my chip is broken or if there is another reason. Would be good to know because my Dell 7586 is brand new.
To make the long story short: With my new notebook I couldn't initially connect to my wifi whereas my android phone and old Win7 PC as always still worked fine. I updated drivers for my router (Alcatel HH40V) and chipset (220.127.116.11), made sure that my wifi was the ONLY one nearby (so no interference) by checking with inSIDDer. I then checked all the channels and different modes manually for 2,4 GHz and found out the chip is not working in any channel of 2,4 GHz in 40Mhz n-mode (but in b and g), but does work fine at 2,4 GHz in all channels and modes at 20 MHz. I didn't test 5 GHz because it wasn't supported by the router.
PROBLEM 2: the current driver 18.104.22.168 can't properly manage the n-mode settings.
I initially wanted to completely turn off n-mode and just keep the a-mode turned on (as this is not supported by my router) to be 1000% sure that my problem #1 is indeed linked to a malfunction of the chip in n-mode. Surprisingly, the driver settings are not working as one would expect.
Of course I had already checked https://www.intel.com/content/www/us/en/support/articles/000005544/network-and-i-o/wireless-networking.html to see the recommended settings but it took me a while to realize that this article is actually saying that one should ignore the options offered by the driver settings and should not expect them to be working because "The setting 802.11n Mode is available only for the following legacy adapters" and the AC 9560 is not listed there. Which is quite foolish if you have a driver that lets you set "wireless mode 802.11 n/ac" to "0. disabled" or "1. 802.11n" or "2. 802.11ac". Having understood that it is not surprising that the chip behaves in a totally different and unpredictable way (n-mode is randomly turned on/off, just as if the option to configure "wireless mode 802.11 n/ac" wouldn't exist at all:
selecting "n" should switch the supported mode to "n", but if you double check using cmd "netsh wlan show drivers" you'll find out that the "wireless mode 802.11 n/ac" does have no effect - if you use "disabled" and "ac" you'll still find "n" popping up. On the other hand "n" wouldn't show up (though set to active!) if you select "wireless mode 802.11 a/b/g" - "b" or "g" or "a/g", but always shows up in "b/g" or "a/b/g" no matter if it is actived or deactived!
I think this is a foolish way the driver settings work (or simply don't work) I would suggest to include a bugfix in the next driver update.
Concerning my problem #1 I would really love to know whether this issue is linked to the design of this driver (and this malfunction is the way it should be) or whether it is broken ... Who can help?
If you do have this chip it is appreciated if you test it with the same values.
Otherwise, please stay away from my post if you have nothing meaningful to contribute.
I am not interested in warranty, I am only interested in the intended functionality of this chip/driver.
Regarding "problem 1", the support guys at Dell don't know whether this is a normal behavior or not. So what do you say now - I've been there, done that. Replacing the chip would only cost me efforts if the next one has the same issue. If you have ever in your life tried to contact any customer service than you might know how time wasting it is to get nonsense answers from people who have no detailed knowledge. And if you are familiar with the fact that 40 MHz at 2,4 GHz is causing loads of trouble and that there is ever since an ongoing discussion that it should be abandonned one might suspect that this chip is maybe just working as intended by Intel. And if I want to know which function it had been designed for, than it surely is the best to ask the designer himself (which I would love to).
Regarding "problem 2", I see Intel staff reading and posting here, therefore I chose to mention the driver layout/settings here which is surely the better place than Dell as it is a general issue for this driver.
You do not make demands here. You have been advised as to the proper support path. You can use it, or not.
And, you neglect to realize that Dell may have made modifications/customizations to the driver.
Also, provide your OS VERSION and build, with the processor model number.
And, you should use only the driver provided by dell, unless they explicitly tell you different.
And, is the 9560 part of your original laptop configuration, or did you add it yourself?
Answer all questions.