Thanks for contacting the World Warfare support team, we are here to assist you.
The issue with turrets failing to deal damage on the rebels is a known issue, and our Engineers have adjusted this in such a way where the server is forced to calculate damage in the situation, so this should not happen as often. We should have this completely resolved in a future update. If this does happen next time you can try deploying some troops out to kill them.
Please also feel free to describe what turrets are not dealing any damage, when you notice this happening and a location (coordinates).
Thanks and sorry for the inconvenience.