As established by the newer canon “Star Wars” comics, Lobot worked for the Galactic Empire at the height of their power. While doing so, he was implanted with the AJ^6 cyborg construct, which helps increase the wearer’s productivity and efficiency. In Lobot’s case, it helped him with calculating conflict outcomes. However, this cybernetic piece immediately tried to restrict the character’s personality in the process.
Eventually, Lobot abandoned the Empire and began working with Lando Calrissian. During their travels, the former managed to maintain control over his implants. However, tragedy struck when Imperial Royal Guards attacked and injured him. Further exasperating things, the ship Lando and Lobot were traveling on was close to self-destructing. The latter was able to activate the ship’s escape pods, but this allowed the AJ^6 cyborg construct to completely take over his mind in the process.
This explains why, by the time fans meet him in “Empire Strikes Back,” Lobot is a mere silent aide to Lando. It also clarifies how the former smuggler is able to “activate” and control Lobot from afar.