The invincibility glitch just happened again during my Rancor Defence. You can see Leia is standing on a destroyed wall – the two rancors cannot touch her so she kills them both.
What is your defence strategy against them? I like using Luke/Chewy/Kessen and in squad centre 4 speeders 2 snipers. I try to deploy so the heroes and troops go through the buildings of my base – giving them more cover.
Good luck catching them!