[Suicide Junkie]

There are some things even that can't fix.

What would the AI do against completely undetectable frigates? Players could use small mine fields in strategic places, behind their frontlines. Thus, blocking sweepers with warships, and allowing the tiny cloaked ships (too small to be effective sweepers) to pass by the fleet and hit the mines.
Against an AI, you'd be able to cruise through their systems with impunity.

It would also completely ruin things if you could capture a resupply depot, or get a military alliance with an AI who has some.