exchange free busy irule for hybrid o365 deployments causing a http 400 bad request

We are testing to access the URL: https://autodiscover.domain.com/autodiscover/autodiscover.xml

When using the free-busy irule(to disable APM for few specific URLs ) recommended by f5 for this deployment we see a 400 HTTP BAD REQUEST. 

irule kb article - https://support.f5.com/csp/article/K34862994

Also, at the same time we see in the LTM logs APM is being disabled( using the irule mentioned above ) for this URL (above) as is the requirement. 

reallyy getting nowhere with this as of now .. any ideas please??