Issues with Outlook Web Access Login Options configuration on APM Logon Page

I have deployed an F5 LTM configuration based on the F5 Deployment Guide for Exchange 2010/2013 with the addition of the following APM configuration for setting OWA Public/Private and Light Version flags.

https://devcentral.f5.com/articles/add-outlook-web-access-login-options-to-the-apm-logon-page

After adding the options for Public/Private and Light Version on the APM configuration it is causing the browser session to pause for an extended period of time (>30 seconds) or timeout completely after successful APM authentication.

• If the browser session is manually refreshed after the APM authentication and during the time the session seems to be paused the Outlook Web App site appears instantly with the Public/Private and Light Version settings applied.
• If the APM Forms SSO configuration is returned to default settings (without the flags and trusted variable names in it) and leaving the iRule in place there is no pause.
• I implemented logging in the APM flags iRule and ensured it is being executed and that the flags and trusted variables are being set as expected.

Does anyone have any advice on this issue or on how I can diagnose further?

Thanks in advance.