Thanks. I'm using version 0.51. Was quite hopeful it had something to do with IPv6 as we have a mix of sites on v4 and v6, however, the site in question is still on v4 and other sites on v6 are working ok. Possibly have narrowed it down to browser - it seems users in that site are on ie9 where as all others are ie11.

Not sure if theres anything further I can do really as I don't have any control of the browser versions.

Thanks for the advice!