Roundcube Gateway Time out when in pfSense Fail over Mode

[ITIstudios]

I have recently discovered that when operating pfSense Fail Over mode Roundcube authentication fails with a "gateway timeout".
Everything on all servers is working as it should.
The roundcube login screen appears but when you submit it eventually returns a gateway timeout.
(this is only when pfSense is operating through its backup firewall)

Not sure if this is a pfSense issue or a Roundcube issue.

Any advise on how to fix this is appreciated.

Thankyou