Optimus Prime was a star cadet at the Autobot Elite Academy, that was until an unsanctioned incident at Archa Seven that led to one of his friend's supposed death not far before their graduation. He took the blame for her death. Magnus had thoroughly tracked his progress, finding him a strong potential candidate as not just a Prime, but a potential successor. Most of the time he was caught with a little misconduct around his friends. Magnus felt conflicted about returning either of them to the academy. In fact, most would be punished more severely for their actions. Almost enough to get locked up in the stockade.
Magnus however grew to have a soft spot for the young, heavy potential, eager to prove themselves trio and sympathize with their loss and broken ties. He talked to Optimus a little more asking if he could hear a little more about what had happened before he made his final decision. The young Autobot did but he still was willing to take all the blame. After meditating over his decision he decided to allow Optimus to technically graduate as a Prime but with a dead job as a Space Bridge worker under the guidance of the seasoned medical and mechanical officer, Ratchet.
He came with an offer to Sentinel. Be banned from the Autobot Elite or restart, and instead of coming in an officer he'll start as an enlisted at basic training. This grit Sentinel's gears as well as increases the anger he placed towards his former friend Optimus Prime.