I sometines get this problem on my Ensoniq SD1 and it is always a loose edge connector or a chip creeping out of its socket. I now take the keyboard apart at regular intervals just to re-seat all the chips! Chip creep is caused by the chips heating up and cooling down again.

It is quite possible that movement of this nature could happen in transit.

Similarly we used to have a computer in the office that would periodically not boot up. Lid off, waggle all hard disc connectors, lid on, computer fixed again!