RE: TB16 constant flicker at 60hz (XPS13 & 4K Dell P2715Q)
I have the same laptop and same dock, but I have an LG 27UD68-W (27" 4k monitor). I use both the external monitor and the laptop screen at the same time (extended display). The monitor has two HDMI inputs and a full size display port input. When I connect the monitor using only a display port cable, it connects at 60hz and full resolution, but it goes black for a few seconds every so often. Sometimes it loses the signal completely and stays dark, and then maybe a while later it will just turn itself back on out of nowhere. If I connect the monitor using an HDMI cable, it doesn't cut out, but the refresh rate is limited to 30 hz, which makes my eyes bleed. Hilariously, if I connect the monitor using both an HDMI cable and a Display Port cable and tell the monitor to display the signal coming through the Display Port cable, I get something in the middle where the refresh rate appears to be above 30 hz, but it isn't quite 60 hz, and it stops cutting out. When I do this Windows thinks there are two external monitors, so I tell it to mirror the displays, which seems to work. When using this setup the Intel HD Graphics control panel tells me the displays are in "Hybrid" mode, or something like that.
It would be really nice if there was some way to get this monitor to just use the Display Port cable and a refresh rate of 60hz! The documentation for the TB16 and my laptop make it seem like this should be possible, but I just can't get it to work. Tech support has done everything from replace my logic board and wifi card to have me completely wipe the computer and re-install. I wish someone at Dell who knows what the heck is going on would explain this to me.