my initial thought was probably slow keys were enabled.

          https://forum.kde.org/viewtopic.php?f=66&t=36625

Slowkeys is not enabled.  This is NOT keyboard specific.  It is affecting a USB hub, flash drive and USB IDE hard drive. 

This issue seems to affect all devices connected to my USB3 ports.  USB2 ports appear to work OK.  Might be a coincidence though.