iApp for Exchange CAS Load balance Method Doesn't Works for OWA Pool

That seems odd. Any request that contains a BIG-IP cookie should bypass the fallback persistence method and be forwarded directly to the pool member address that's hashed in the cookie value.

Is it possible for you to add the fallback persistence back in, and look at the OWA request in something like the IE dev tools or Fiddler? I'd like to know if those clients either don't send a BIG-IP cookie, or if they do send the cookie and BIG-IP is not processing it correctly.