An update to my problem.
The solenoid was replaced with a new one, and that didn't fix the problem. Tractor would start intermittenly, but not reliably. Dealer picked up tractor and kept it a week troubleshooting. They got the tractor starting consistently, I think just pulled connectors and cleaned, nothing was replaced.
I used the tractor last weekend for the first time since getting it back, after about 30 minutes it just shut down as I was driving then started back up fine. In a couple hours of work, it shut down around 30 times. Sometimes when trying to restart, the solenoid at the injector pump would just buzz instead of click open, but I was always able to get it to restart eventually.
Dealer picked the tractor up again Tuesday morning and has replaced several relays per Kioti's instructions, should be back today.
This is the 3rd attempt to fix the same problem in 2 months, hope they get it right this time.