The only problem I have had was at JFK some years ago.
My wife, a pensioner, cannot walk without shoes due to fused ankle bones.
I called the supervisor and he was deaf to my reasoning.My wife just about managed with a lot of pain and anguish to get through the arch.
I asked him why folks in trainers were not going through the scan. No response.
I assume it is about some women's shoes having a steel shank in them . Perhaps the supervisor was never told about this.