I think it is a matter of chance, possibly a policeman and/or ticket taker at one station is enforcing it, in another spot they are slacking off.... I had the same issue where I brought in dunkin donuts coffee for years, then all of a sudden, they did not want me
to bring it in....so I have not tried since.
anyway, I am bringing in two pp & j sandwiches wrapped up, in a coat pocket today