I've swapped the two monitor connections with each other at the back of the card; the higher resolution has now moved to the opposite monitor. This confirms the problem is not with either the monitor or the cables.

So plugging in the monitor that was running at 1080p into the DVI-I port allows you to run it at 2560x1440? If yes, it does sounds like the card has a problem. Have you tried to clean your video cards drivers out with ddu, and then reinstall the video card drivers clean to see if that would resolve your issue?

Additional information: I'm using Nvidia's GK208B driver for GeForce GT710, for Ubuntu. from the driver metapackage nvidia-driver-435.
 

Jim.C
Additional information: I'm using Nvidia's GK208B driver for GeForce GT710, for Ubuntu. from the driver metapackage nvidia-driver-435.
 

Not sure how to do a clean install of the drivers on ubuntu, but you should definitely try to do that if you know how to do it on ubuntu.

Another thing you could try would be to install windows to see if you can replicate the issue in windows.

If I go back to the generic open source driver provided with Ubuntu (X.Org X server), it doesn't recognize the secondary monitor (the one on DVI-D) at all. I don't have a Windows installation available for this machine. I'll research removing the driver and re-installing a fresh copy. Thanks for your help.

No problem. It really does sound like a card or driver issue at this point.

I've found an acceptable workaround to this problem. Instead of driving the second monitor with the DVI-D output, I'm instead using the mHDMI output. I'm now able to drive both monitors at 2560 x 1440 resolution. The card is less than a month old. If you think I should exchange it, I'd like to know how to proceed.

Glad to hear that. Are you ever going to use the dvi-d output in the future? If yes, it would be a good idea just to rma it before your warranty runs out.

It seems this thread refuses to die...
 
I got this morning an Asus GeForce GT 710 2GB GDDR5, and inmediately tried to connect my three very old VGA monitors, with these resolutions, totals, and result substracting  8,294,400:
 
1,2801,024 11,310,720  1,440900 21,296,000  1,2801,024 31,310,720       3,917,4404,376,960 
The card has 4 HDMI ports, and I bought three HDMI to VGA adapters. Probably I understood something wrong, but I can not connect but two monitors, and, connecting the third, the three of them failed and had to restart.
 
And I was dreaming of a forth!
 
I work with online sheets and the monitors are real life-savers
 
A bit desperate, two monitors is a really low number. I had three in my old setup, used one port of the motherboard, but now it is not possible because this CPU has no graphic procesor. Really lucky.
 
Can I connect my old graphic card at the same time? This way I would have more ports and processing capacity.
 
Ideas? 
 
Thanks a lot
 
Max