U2515H flickering in multiple monitor setup

I am not sure why you are using HDMI to mDP cables?

The 2012 Dell OEM Quadro NVS 510 has the following video out ports =
mDP, mDP, mDP, mDP

You should be testing using the mDP to DP cables that shipped in the U2515H boxes.

Quadro NVS 510 mDP #1 out --> U2515H mDP to DP cable --> #1 U2515H DP in
Quadro NVS 510 mDP #2 out --> U2515H mDP to DP cable --> #2 U2515H DP in
Quadro NVS 510 mDP #3 out --> U2515H mDP to DP cable --> #3 U2515H DP in
Quadro NVS 510 mDP #4 out --> U2515H mDP to DP cable --> #4 U2515H DP in

And have you moved the flickering monitors to different ports on the video card?

Hi Chris, my mistake...  The cables I am using are the included DP cable (mDP-DP).  For some reason my brain saw the DP end and thought HDMI.  

Yes, we have swapped the ports.  Just an observation, but the problem seems to always occur on either the 1st or the 4th monitor (either left or right edge of the 4 ports on the Video Card).  Another odd observation, but when we swap the cables to different ports, often times the computer will recognize that the monitors themselves haven't moved and keeps the display identity the same (when it assigns the display number to each monitor, seen by clicking Identify in Display Properties).  

Let me add a little more insight.  We have an office of 40 machines and each have the same HW, although some users have 2, 3, or 4 of the Dell U2515H.  So far, the stations that only have 2 or 3 monitors do not seem to be impacted. A handful of workstations with 4 have reported the flickering on 1 or 2 monitors), or the monitor just going black (always the same monitor, and the computer still recognizes that the monitor is connected), and in order to view the screen you have to disconnect and reconnect the DP cable. Currently, about half of the 4 monitor setups are intermittently impacted.  

So, you can disregard the issue of it being isolated to monitors connected on either of the edge ports on the card.  We had an issue this morning where the 2 bottom monitors for a station were flashing, and they were in the 2 ports on the right.  

Could it be an issue with the video cards themselves?  Or, does the fact that the monitors are consistently recognized by the computer a sign that the ports on the video card are operational?

I have found what appears to be a solution (previously provided by another user, on another thread), but the real proof will be tomorrow morning after the nightly reboot of the machines.  

Removing the USB 3.0 upstream cable, from the monitors has stabilized the imaging.  I believe our desktops only have USB 2.0 ports, although I am not sure if that is a contributing factor.   Fortunately the users were not using the USB ports on the monitors themselves.  

I will reply again in the morning, to confirm if this resolved the issue.

Well, the problem appears to be lessened, but still persists.  When the user came in this morning, after the nightly reboot, the issue was present.  The 2 monitors were power cycled, which seems to have mitigated it again.  So, disconnecting the USB seems to have greatly improved performance, however, the issue is not truly resolved.  

Chris M,

Do you have any ideas what may be occurring?  Any other information I can gather for you, or troubleshooting I can take to help narrow down cause?

It appears that DP 1.2 enablement was the key!  Both stations where I enabled DP 1.2 on each monitor were stable this morning, when they were consistently failing previously.  Thanks for the input, Chris M!

FYI, I believe all monitors are A02, as that is what is shown on the remaining boxes we have.  The other boxes have already been recycled.  Is there a way to confirm in the monitor menu itself, which revision I have?

Now I am confused. DP 1.2 should be disabled on both if you are NOT daisy chaining them together. But in your case, even though they are not daisy chained, enabling DP 1.2 on both helped. The label on the monitor itself is the only way to know which revision it is.