User authentication issues in Outlook

Hm..when you say a single VIP, that's a single VIP for HTTP-based services, and then another VIP for RPC, correct? Are you doing SSL offload on the F5? I would recommend trying to remove advanced profiles from the HTTP-based virtual (everything but SSL profile) to see if it addresses the issue - if it does, we'll know better where to troubleshoot. If OneConnect is enabled, I recommend turning it off first and see what happens.