I had an issue simila tot hat. The Jaguar has an internal storage once that's filled up it can't harvest anymore unless it can empty it into a trailer. Now my issue was that one of the trailers had to almost be directly under the pipe in order for the jaguar to unload into it. Now I didn't sent the trailer away, I continued to fill it up and then I sent it away, after that I had no issues with either of the tractor's and trailer's. So try and sent that tractor and trailer you are having troubles with away and request the other one to come and help you.

I'm not sure what would cause this issue but I'd recommend to remove your savegame just to be sure it's not related to that.

Had yesterday something similiar, loaded a saved game but then i wasn´1 able to harvest anything no matter what.

Sold the vehicles and bought new ones and it worked without any issues

Aah yeah, I had an issue just like that after saving and loading a game. Pipe couldn't find the trailer(was aiming behind it). I tried to sell and buy the jaguar+header didn't do anything, but I suspect it could be the trailers that got glitched because of loading the savegame

Edit: I just had the same issue, and I can say that buying a new trailer and hooking it up to the tractor will fix this issue.

Happy harvesting

F1 -> Vehicles -> Fleet -> Sell