you try restart services ?
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have you narrowed it down and tried on just one host?
can you generate bundles from the console (didn't see ESXi)?
can you post the vpxd logs from vCenter? usually those logs have more data from vCenter telling you what the problem is. also you can take a look at /var/log/vmkernel and /var/log/vmkwarning and hostd logs on esx, if this is a console version. can you post a screenshot of the error?