I bought two XPS-13 laptops which were both pre-installed with windows. I have since partitioned and installed Ubuntu on both.
One of the laptops had persistent wifi issues disconnection issues. The wifi on the problematic machine was also unreliable at resuming from suspend, and had poor range. I was also seeing many PCIe bus errors in dmesg.
In an attempt to get some stability, I tried everything, from firmware, bios kernel versions, kernel/module parameters.
In the end I decided to replace the wifi card with an Intel 8265, which has worked flawlessly since installation. One thing I did find while removing the killer card, which could be related to the poor range, was that the tension in one of the antenna coaxes had detached the barrel of the connector from the killer wifi card. the card was also not installed squarely within the pci express socket.
As for the other laptop, which has exactly the same operating system configuration; the wifi hasn't had any problems whatsoever.
So I think it is just "luck of the draw", my guess is that a certain batch of the killer cards have a poor manufacturing yield.