Hey there @DiploQuin! Welcome to the community!
I’ll give some general tips, but if you can show us your blueprint and explain your use case we can probably correct it right then and there!
My first thought was, where are you casting and to what? If you’re having trouble with casting to the player, (and there’s only one) the easy way is to use Get Player Pawn and you don’t need to cast to get it’s actor details.
However if you’re trying to cast to the AI to tell it when to start chasing and when to stop chasing it’s somewhat more dependent on how your game is set up. You need to get a reference to that AI actor before you can cast to it, and from your description you might be doing room based horror so you could get away with assigning that reference when the AI is spawned.