The SAME ( Hurliman 435 branded) that I have Does the same thing!
'Just shuts it's self off and sometimes doesn't want to restart. There was another TBN member who posted a similar issue some time back.
In my case, I can hear the fuel shut off valve "clunk" open when it's ready to restart. I have never had the issue starting from cold at the beginning of a use session.
With only those few symptoms, I believe there is a problem with the Engine Stop Solenoid Control Unit. A "black box" that controls the fuel shut off solenoid, and resides under the steering wheel cowl on the station side of the firewall.
The Hurlimann is fitted with a Mitsubishi engine. If you have the Deutz engine, the unit may be called something else.
I once put in some effort to try to get one of these units from a site supporter who seems well connected with Mitsubishi tractors, but not so much the SAME. At the time I wasn't "willing" to pull the cowl to get a picture of the unit to accurately describe it for possible replacement. I'll pick it up again if the problem gets to be too great an aggravation.
Like your tractor. Sometimes it's a few minutes, but more often it shuts down once every few hours.
"The Dealer" is at least 3 hours from where I am, at least I haven't found one closer. And so far, I wouldn't throw $100 bills at anyone I've talked with trying to get a straight answer on this problem based on knowledge.
Do me a favor. When the engine dies, Listen for the fuel shut off solenoid opening again. And then try to start the engine. If it starts right up, our issues have very similar signs and symptoms. It would be difficult to hear the solenoid over the sounds of a cranking starter.
It would be fun to figure this out. There are three tractors with the problem for sure....
ETA
One other symptom in the case of my Hurlimann, There are times when the shut off will NOT activate when turning the key switch to the off position. This happens rarely, but enough so I've got the location of the mechanical shut off lever on the pump down well enough to find it in the dark. ;-)
Second edit
After a search, I note that you had posted this problem in 2015. So it's the same SAME ;-)
Only two tractors with the issue, not three..... ;-)