I’m not sure if you have figured this out yet, but I found this thread by having the same issue, since there was no clear answer here. I fumbled upon this fix out of pure luck. The character you are trying to cast from “AI controller” isn’t set to the right AI controller… confused yet? uh… just do this.
Click on the “top root (self)” on the componants tab, then in the details panel scroll down to pawn, then on the AI controller class, its default is AIcontroller, click the little black aarow and scroll down and find the AIcontroller you created. After selecting it, you will see a quick “building” popup. Now, in the event graph, pull off the GetAIController return pin and search your “cast to” and you will see it. Hope this helps! 