Issues with Exchange 2013 owa

Hi Perry, good to hear it's working. But the fact is that for Exchange 2013 it should be working fine without any persistence:

(Source: Technet)

Load Balancing

Unlike previous versions of Exchange, Exchange 2013 no longer requires session affinity at the load balancing layer.

To understand this statement better, and see how this impacts your designs, we need to look at how CAS2013 functions. From a protocol perspective, the following will happen:

1. A client resolves the namespace to a load balanced virtual IP address.
2. The load balancer assigns the session to a CAS member in the load balanced pool.
3. CAS authenticates the request and performs a service discovery by accessing Active Directory to retrieve the following information:
    Mailbox version (for this discussion, we will assume an Exchange 2013 mailbox)
    Mailbox location information (e.g., database information, ExternalURL values, etc.)
4. CAS makes a decision on whether to proxy the request or redirect the request to another CAS infrastructure (within the same forest).
5. CAS queries an Active Manager instance that is responsible for the database to determine which Mailbox server is hosting the active copy.
6. CAS proxies the request to the Mailbox server hosting the active copy.

Another handy article about this is on Kemp's website: https://kemptechnologies.com/white-papers/what-know-about-exchange-2013-and-Load-Balancing/

That is why we changed from different per-CAS-server self-signed certificates (like in Exchange 2010) to one and the same SAN certificate on all CAS servers, containing the names of all CAS servers and the used URLs. This makes changing to another CAS server possible, and it solved our problem with rebuilding connections between LTM and CAS, and thus producing re-appearing logon screens.