For item 1 above, check if you can ping the Managed Host from the Central Server. If you can, then check if the xprtld service is running. If it is, then the problem might be item 2. If the solution for item 2 does not solve the problem, contact Symantec Technical Support.
For item 2, run the following command on the Managed Host:
/opt/VRTSsfmh/bin/xprtlc -l https://localhost/world/getvitals
Determine if the central server name appears in the command output in the domain section. If it does, contact Symantec Technical Support.