I'm encountering a bug where on some levels, a freeze activated tower will freeze an enemy right at the beginning of the path and then not clear it. The animation loop for the enemy continues to run. I can still complete the level but it won't show up as completed on the map. It also seems to happen when I'm standing to the right of the enemy instead of the left.
I've been able to move on by avoiding using freeze weapons at the start of the path and standing to the left of the enemy.
 "Royal Protectors"){kind=icon}
 "Castaway Island TD"){kind=icon}