Scout Towers in Blight Encounters

Recently ran a Cemetery map with a random blight encounters. Using the Scout and Empowering tower strat, I noticed my scouts would not engage in combat until they were fully upgraded to sentinels. I neglected to snag a screenshot unfortunately as the encounter ended shortly after I noticed why I was getting overrun. The encounter spawned mostly arachnids if that's of any help.

ok that explains why I keep failing Blights.

This is not just in Cemetery. Iv had 3 encounters that the mobs just walked right to the Pump. No towers affected them. Only my attacks but they are Beefer then any other mob in the map. Like they were empowered but I didnt use my Sentinels on them (tho I did in the map)