Bad front/rear switch or wires. The meter probably was used with the switch in the front input setting. I have replaced 3 of the switches and one cable. They were all related to the switch and/or wiring breaking at the crimped ends of the cables. It is a tight fit between the switch and chassis.
The folks at Loveland are good people, I hope they spare you the high dollar repair. Either way, having the extended warranty is a good investment. They also provided me a 5 year, but I had to ask for it. It isn't something that was easy to find at the time of purchase.
I currently have a 3458A at that lab waiting for cal after some repairs were made.