Check your UI settings and turn on the option to "Always Show Resolve." This will allow you to see your enemies resolve under their health bar.
Certain CC abilities will fill ones resolve: ie. stuns, long duration CC (the 1 min cooldown ability), etc. This is just the ones I noticed.
When we use our knockbacks, they DO NOT effect resolve, BUT if the enemy has any resolve left your knockbacks WON'T WORK.
So, just FYI, when you're pvping, knock back first.. then stun.
Also, you must wait until the enemies resolve bar FULLY goes away or your CC won't work.