If you look up the ID in v5 you’ll get the following {"error":"Unprocessable Entity","status":422,"message":"User \"29325630\" is unavailable"}
Which would indicate the user could have been banned, suspended, deactivated, or maybe something else. I would assume that the reason it remains in a list of follows is that the condition causing the account to be unavailable might be temporary, and if a banned account would be unbanned it would continue to have all of it’s previous followers instead of losing them all.