TB15 and WD15 - along with anything connected to the USBC/TBolt port
I also have endured the saga of the Dell (in my case a fully maxed 9350) flaky USBC/TBolt port.
I had a TB15, but eventually sent it back. Although fully capable personally, I refused to extensively modify a fairly expensive device that should be working.
So, I tried a WD15, only to have it be as unstable as the TB15. The TB15 had the incessant display disconnect/connect problem, as well as Ethernet issues. The WD15 would repeatedly disconnect/reconnect any USB3 devices. The P&P tones were maddening.
I discovered that a USBC to USB3 hub would also disconnect/reconnect incessantly. A USBC to Ethernet dongle was unreliable. The only thing that seemed stable was a USBC to Ethernet dongle.
The various driver and BIOS updates incrementally fixed issues. Finally 1.4.4 seemed to give me stability. But.... I had to put the machine in airplane mode to have any stability when the WD15 was connected.
Reading here, I ordered an Intel 8260 Wi-Fi/Bluetooth module and replaced the Broadcom card. After figuring out the problems with switching modules, I now have a properly working 9350/WD15. I have put it through it's paces with various combinations of airplane mode on/off, docked/undocked, etc, etc and I am close to pronouncing I have this fixed.
One note: you have to thoroughly remove all Broadcom drivers, etc. This includes the Widcomm stack.
I strongly advise Dell - and those reading here to ditch the Broadcom POS and install the Intel 8260. They are only ~ $25