>>529998841
The friends that show up for those training sessions are entirely dependent on your support cards. It can be R, SR, and SSR. I'm running all SSR cards, and those 5 reflect 5 of my support cards. Spe fucked off somewhere else, didn't go look. Sometimes friends just don't show up at all.
It is pure rng, unless someone knows how the game thinks and can force it, I guess.