Oh dang!
Well, I was already aware of some "invisible" enemies in the tutorial but now I checked and also encountered the "invisible & undefeatable" enemy type 😐
I'll have a look for the next update. Thx for pointing that out! 👍
(P.S.: The version doesn't matter here 😉)
Did you try to push the spawn button several times? You just need to kill 1 enemy in the tutorial to be able to advance...