Computer: Dell Precision 5520 using latest Intel Driver where 8-Bit works.
Dock: Dell WD15 with 180w PSU
Monitors: Two brand new out of the box Dell U2518D's
Previous Monitors: Two Dell U2415
I have setup dozens of pairs of U2415's in a Daisy Chained configuration without issue. A colleague acquired two U2518D's and attempted to set them up in a Daisy Chained configuration and found that he could not get them to extend, only mirror. I was also looking at these monitors and since I have a lot of experience setting up U2415's (and U2414H's before that) we decided to order another pair for me to test. Unfortunately I am having identical issues to my colleague.
I swapped out the U2415's I already had with the U2518D's so they are connected correctly. On the primary display I have enabled MST and DP 1.2. I have attempted disabling DP1.2 and MST on the second monitor with no change.
In Windows, I cannot get the computer to recognize that a second display is connected. I have read as much materials as I can find on solutions but all of them ultimately point to DP1.2 and MST. Now we have four monitors that are effectively useless because we cannot extend them.
I tried plugging my U2415 back in and was able to get that to extend to a U2518D as long as the U2518D was the secondary display but the resolution was incorrect and being that they're not a matching pair is not ideal anyway. When I swap it so that the U2518D is the Primary and the U2415 is secondary, the U2415 does not detect a signal. I disabled DP 1.2 on the U2415 and was able to get it to tell me the resolution was incorrect, which makes sense being that the U2518D outputs a much higher resolution.
So here is a break down of what I've tried and the result.
[U2415] - [U2415] = Extended
[U2415] - [U2518D] = Extended, wrong resolution
[U2518D] - [U2415] = Error on U2415 about wrong resolution
[U2518D] - [U2518D] = Only Mirrors, regardless whether DP 1.2 is enabled on the second display or if MST is enabled or disabled on the primary display.
Using the latest Monitor Driver and Firmware for the U2518D.