I found out that an underpowered USB powered midi-keyboard can sound like the pitchbend is rolled off 5% and effect the voltages used.
The first thing I tried to do was to factory reset the keyboard, but the problem persisted. It was only when I saw a midi keyboard m32 by Native Instruments that was displaying the fractions that the lack of voltage was doing to my signal.
Simply making sure the keyboard wasn’t plugged into a USB hub seemed to work. Usually I’ve found if you are dealing with bus powered devices then 2 inputs off a USB hub is all I can do. I tried one powerd hub, but didn’t have much more success. Hope it helps.