Tower slots not unlocking fully even when maxing maps with 6 affixes on them

I have done 2 towers so far, and maxed out the maps with 6 affixes and even went back to ensure I couldn't add any more to them. The 3rd slot never unlocks, even though it tells you to unlock it, use a map with 6 affixes on it.

Twice now this has happened, and there is literally no way to bump up the maps beyond 6 affixes, but they are not counting apparently and needs to be fixed.

From what I can tell, I have no way to go back and try these towers again once they are unlocked, but am hindered now because the 3rd slot is not unlocked as it says it should be.