1 Nickel

RE: U2417H, DP 1.2 daisy chain mirrors, but does not extend.

I had this exact same issue with Dell U2717D monitors.  The monitors were mirrored and showed up in the display manager as one single monitor.  I played with enabling/disabling DP 1.2 on the second monitor to no effect.  Finally I found out that there was another setting in monitor configuration that was simply called "MST".  Evidently this is called "Multi-Stream Transport".  Once I ENABLED MST (in addition to DP 1.2) on the first monitor, the displays un-mirrored themselves and Windows treated them as separate monitors.  Enabling DP 1.2 and MST on the second monitor allowed me to daisy-chain a third monitor.  They are all recognized as 3 separate monitors and can have independent resolution settings.  At least for me, MST was the key.  The MST setting on the U2717D is under DISPLAY -> MST.  For me, at least, this fixed the issue of the displays mirroring while daisy-chained.