Barcelona is getting over-run, or so some residents are saying (30 million visitors in 2016). It's become a huge hit with tourists from Asia. The mayor, Ada Colau, has also made statements saying she doesn't think the city can't cope any more.

However I don't think its connected with this directly, since passport control - which only affects non Schengen travellers - is handled by the Cuerpo Nacional de Policía and Guardia Civil, which are both under national control. El Prat may be getting over-stretched however.

[Doesn't affect back to back passengers, there is no passport control].