Not sure if the Grobo team will see this prior to Monday. I don’t have my Grobo so I can’t offer you any suggestions beyond rebooting the Grobo and seeing if the fans come on.
In my growing experiences fans are used to circulate and bring fresh air in. In my case I also had exhaust fans to suck out the hot air created by 1000w high pressure halide and sodium bulbs for bloom.
I wouldn’t worry to much about the fans not running while the lights are off. If It gets to warm in there I would suggest opening the Grobo door and aim a desktop fan in the box replacing old stale air and cooling it off. Close the door and repeat as neccessary until the team can address your fan situation.
Moral of the story is a couple of days of no fan circulation shouldn’t harm the plants if you can keep it from getting too too hot in there. Don’t worry to much they are resilient.