I have problem same your and still did not found a solution.
Hosts inside still working fine ( i can remote directly by remote desktop or teamviewer),
and services inside host working well.
Problem just cannot login by vsphere client.
If I restart ESXi, I can login again.
I see some issue before this problem in system log, It like root@127.0.0.1 login fail many times.
I think it maybe attack from someone but nobody use login at server at that time.
If someone can help me please tell.