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Recently I encountered this problem in a customer site whereby the logon to VCSA 5.5 would either time out, or take 3-5 minutes to actually log on.
Running a netstat on the VCSA during the attempt to logon showed there was a SYN packet sent to the vCOps appliance on port 443 that never established a connection. Another check was attempting to connect using curl <https://
Ensuring connectivity to the vCOps appliance over port 443 fixed the logon timeout issue – presumably a the connection attempt holds up the logon process (single threaded?!) which causes a timeout in the logon process.