Increased hack chance or reduce Cooldown before first successful hack.
Increase control time, reduce Cooldown for small enemies.
Reduce hack chance and cooldown for large enemies.
Add a hud notification that skill can be used again.
Add hack failure notification.
Binocular tech view should be more transparent.
You dont need a notification to see if your hack was a success or not. A hacked machine has a faint blue glow.
I’m playing with a friend, I’m not the host. It often happens that the color does not change, but the hack is successful.
You should make a bug report for that. 
Good observation.