Does your host profile include stateless caching? And if so, how many SAN volumes are presented to your ESXi 5.1 hosts?
I ask because we have an escalated support ticket with VMware where we determined any ESXi 5.1 host with a large number of SAN volumes presented to it (in our case, 32) had problems applying the host profile on startup.
If you do have stateless caching enabled, try disabling it in the profile and see what happens.