Good question! I'm on PC. If I reload to a way earlier save pre-Monastery, his movement is normal. It happened somewhere in the Monastery (many many hours ago).
I've killed him and Withers-rezzed him, still just stands in one spot.
May be related, every time I talk to him I get the same dialogue options,
"Councillor Florrick confirmed your dad is in Moonrise towers, we gotta go get him"
