I had that problem, asked the admins for help, and was instructed to use the "Remember Me" (or stay signed in, whatever) option. That solved
That was happening on almost every website I accessed... at the time. Has happened a few times, since then, but it only seems to happen from a few different access points. IOW, it doesn't seem website specific, but rather something to do with how an access point/router/gateway is set up.