Untargetable Djinn

While playing Royal Gardens on nightmare survival I am encountering an issue with a Djinn that my defenses will not target. He despawns eventually, but wrecks the place first.  Is this an intended thing? Recently started playing on computer so I am starting over, but I don't remember having this issue on Playstation. 

If I start from scratch he usually shows up on wave 3 or 4. If I do a wave 20 or 23 restart he shows up on the first wave. More of an annoyance than game breaking, but it's still a big annoyance. Has anyone else experienced this?