Do you see any error in the eam.log that points to the VUM issue?
When I had a host preparation issue related to VUM, what I saw on the eam log was:
“com.vmware.vim.vmomi.client.exception.ConnectionException: org.apache.http.conn.HttpHostConnectException: Connection to https://<vCenter_Server_Hostname>:8084 refused”
and 8084 is the port number for VUM
See if restarting EAM as per below blog post fix the issue: