We finally solved the issue of the jumping print head that was impacting several of our 3d printers.  We would consistently get solid prints in the morning or late afternoon, but midday would often see prints start to shift horizontally or vertically as the bot moved to higher levels on the z-axis.  After experimenting with dozens of fixes — from cleaned power sources to shorter USB cables to removing humidity — we learned that the issue was actually caused by overheating RAMPs electronics.

We added a 40mm fan in a bracket mounted over the RAMPs on each printer and the problem instantly went away.  If you notice any issues with the print head mysteriously jumping around, even in ways that appear to be hardware related, give a fan a try.  It is a quick and cheap fix that I wish we had tried first.