Undefined error when switching.

[Almonaster Nuevo]

I generally ignore one-shot errors, but I have recently hit this a few times so I thought it worth reporting. When I use the drop down, fill in my destination and press the switch button, the page just hangs for several minutes, then finally returns....

Web server is returning an unknown error

There is an unknown connection issue between Cloudflare and the origin web server. As a result, the web page can not be displayed.

Ray ID: 8ecb5e7f695594b7
Your IP address: 51.9.205.146
Error reference number: 520
Cloudflare Location: London