Bricks form issue, not always :S

Hi folks, I’m having a really strange problem with a website I developed.

I have a form in Bricks, supported by an SMTP configuration plugin, which works correctly when I test it by submitting it.

But this form sometimes submits successfully, and other times it just hangs and does nothing… it’s really weird.

Could you help me? Hope so…

This is the exact url: Inscripción de actividades y transportes - Salidas Escolares