Diagonal Calipers Dragging, ABS Pump?

[WaxhawFive]

I discovered that my rear left caliper was dragging after sensing it may be for a few days. I used an infrared thermometer gun and found the left rear to be MUCH higher than the right rear, which I suspected, but also found that the front right was also much hotter than the front left.
Focusing on the rear, I found that the caliper piston was very hard to press into the caliper body (EPB motor was removed from the caliper and the threaded activator fully retracted behind the piston for this test.) Digging further, I removed the hydraulic hose from the caliper and discovered that the piston could now be easily pressed back into the body. This points to a collapsed flex line typically, but the diagonal caliper dragging makes me wonder if this is related to a ABS pump problem. Any thoughts?