Ranger – “Defense” [Campaign 5, Mission 3]

I have version 1.1. I freed all the garrisons and collected them – the checkbox is checked. I maxed out all three (and one extra) to level 24. I cleared them all, but the purple one keeps coming back... I've replayed it 4 times already... I've tried everything suggested here... NOTHING WORKS!
Maybe someone knows something else and isn't saying it?
Please help...