Was the leader, the base eliminated?
Otherwise, there are a lot of bugs in the strategy execution unfortunately. A common bug is that ships stick to their stragety for some time, then forget it. Has happend numerous times to me that "Don't get hurt" planet blockade ships headed to the edge of the combat area for the first turns, then turned around and flew towards the planet to get shot down by the weapon platforms.
In crucial situations, I would never rely on any other strategy than "optimum firing range" to actually work, unless you like to gamble
