When assigning someone to man a cannon turret they don't reload it when its empty. They just stand there. You can't order someone else to reload it while they man it because the reloading job is reserved by the pawn manning the cannon.

You have to manually micromanage the reloading of the turret and then reorder a pawn to man the turret again.

Is this intended behavior or is something going wrong here?

I feel like in the past (prior to anomaly DLC being released or even announced) that the pawn manning the cannon would automatically rearm it from nearby steel.