Enemy value is reduced, but then jumps back to full power after an attack

probably a weak unit was destroyed so the average hit points increased.

A good place for posts like this is Bug Reports and Issues, or Questions and Answers.

Conquerer has the right idea. A unit was destroyed, thus raising the displayed percentage value, methinks.

Also, I have moved this thread to a more appropriate forum. In the future, please try to post in the appropriate area.

Another possibility is that you are seeing an Intel image. Images that are captured by spies or patrolling planes are noted on your display by a shadow spy man figure, and when you select the unit you will see the words “intelligence from xx:yy”. These intel images are displayed whenever the area is not in view.

Rockets generally attack the enemy outside of visual range.

So you cannot actually see what damage was done. You need to do a flyover with a plane and gather updated intel on the area.