Are unsecured cafe wi-fi networks deliberately hostile to VPNs?

I’m in Bill’s cafe in Cambridge, which offers ‘free’ Wi-Fi — which of course I don’t trust. So I switch on my VPN to find that, mysteriously, it can’t connect to its server. And I’m wondering if this is just some kind of glitch, or a policy by the firm that provides the Wi-Fi. After all, they don’t want clients sending communications that are encrypted and therefore inscrutable for advertising and tracking purposes. In this stuff, only the paranoid survive.

I had the same experience as John Naughton yesterday and Friday, signed in to the wifi in a bed and breakfast. No matter what, my VPN (Mullvad) would not connect. Rather than go unsecured though, I signed out of the wifi, but it definitely is strange and I think I am seeing something similar more and more often.