I began to observe the many alien fleets moving about my home sector and have watched them take out all the heavily defended anomalies. NONE have them have had a survey ship within their fleets. Do you still need a survey ship to scan a heavily defended anomaly or is the game cheating?
I have seen this also. I can't survey them without a survey ship, so the AI is cheating. One of the recent updates changed something, so the AI now goes after defended anomalies instead of ignoring them.
Once, I was able to use a fleet to attack and destroy the defenders of a lightly-defended anomaly, but I couldn't survey it because the fleet didn't have a survey ship. The AI seem to be doing a variation of this and surveying without a survey ship and doing the survey on the same turn the defenders were destroyed.
I've seen some instances where a single survey ship without weapons or defenses will survey a heavily-defended anomaly without taking any damage. It should have been destroyed.