I've had these two U3417W for a while and was working off a MacBook Pro, which did not support MST.

I'm now primarily working off a Windows computer, and when reorganizing my desk this weekend, was excited by the possibility of being able to daisy chain my two U3417W.

I've got a USB-C to DP cable running to U3417W 1, then the provided DP to mDP cable from U3417W 1 to U3417W 2. I've enabled DP1.2 on both U3417W (I think. The menu doesn't quite work as indicated in the instructions), and turned MST on U3417W 1 ON (MST on U3417W 2 is off, I had to connect it directly to get the menu, but I did check!)

U3417W 2 doesn't display anything at all. U3417W 1 works as expected. But the weird part is that U3417W 2 DOES recognize it has something plugged in (it displays the "No image on this input" message, not the "No mDP Cable" message).

The computer recognizes there are two external U3417W hooked up, in Dell Display Manager as well as System display settings.

It feels like I'm SO close to getting this working. But I have to work tomorrow and if it's not a quick fix, I'll just go back to two separate outputs, one to each U3417W.