Hi Deon,
Try setting ~no_logon_userexit 1
in the WEBGUI 'GUI Configuration'
and then testing the WEBGUI service again.
See the following KBA and Note on this parameter
2082331 ITS login results: "Please wait. You will be forwarded automatically."
1465767 Logon user exit SUSR0001 not called
Regards,
Oisin