Why are two identical external monitors displaying at different resolutions? I have a MacBook Pro (Retina, Md 2012) running OS X El Capitan 10.11.3. 

I purchased 1x DisplayPort to VGA and 1x DisplayPort to DVI.

I plugged these two into the 2x DisplayPorts on the MacBook Retina.

When I view the screens, however, one of them shows up fine but the other is at a low resolution (800x600).

I've seen some related posts, but nothing addressing this situation specifically. Most seem to be dealing with daisy chaining two external displays off of a single DisplayPort, but this MacBook Pro has two ports, so no daisy chaining.

Any thoughts on why the two different resolutions?
My guess is that it's in the DisplayPort to VGA not supporting a high enough resolution–although 800x600 is rather low, there's not a hard rule for VGA. Have you tried switching which monitor uses VGA and seen if the resolution tracks?