Units that have monarch outside the boss event are only placed once by the auto player, but due to having remaining placements, the auto play gets stuck and does not continue on to the auto upgrade stage. You can still manually place those extra units and then the auto play starts working again
I have power and alucard monarch
so when the game started, after placing power once, it would no longer place
then after i manually placed them, it placed all denjis and then stopped at alucard again
and after that once i placed the alucards, all the auto upgrades toggle at once and the auto play resumes like normal