o_O That's really strange, never heard of Jespar going invisible.
The last thing that I can think of, would be to prid him and then disable and enable again, maybe he shows up then? (If I'm right, the prid command let's you target something that's not infront of you, right?^^ So, if you type in prid (Jespars ID) and then disable/enable, maybe that works? Don't think resetai will do anything, but you can try this aswell...)