we had similar issue on ESXi 5.5. and it was caused by bug in AD authentication agent. workaround was to remove ESXi hosts from AD domain (Leave domain).
nowdays it is already patched
At time of issue, are you able to take direct vsphere client session to the host?
I highly suspect this could be an issue with hostd agent which is responsible for all user world tasks. Did you get a chance to check the hostd log ?
post the hostd logs at the time of issue to check which module is causing the issue. I am also wondering why does it not work even after restarting management agents.
I found the following article, check if this helps you
do you have enough space inside your ESXi (log-in to ESXi shell and type "vdf -h"
sometimes missconfigured syslog folder can eat all the space. and then even after restart it doesnt work. but for sure logs from affected ESxi host with timestamps when the issue is observed will be welcome.
I couldn't able to connect host directly from C#client or webclient. verified have enough space on ESXi also.
Each of our esxi host is configured/installed locally and have enough space. Am sure we do not have any space constraint for our ESXi host.
I see the same issue in my environment as well and am looking for the solution. It seemed to start after we moved from 5.5U3 to 6U2 and I only see it on the hosts that have been upgraded to 6U2. (running VCSA 6 fully patched w/ embedded PSC)