VERIFIED SOLUTION i
On starting 'Core' and 'Security' services in EngageOne 4.3, services gets started in few seconds. However it takes time for core components to get functional. For example, it may take around 10 minutes after services start/restart to get response of URL :
The fact that core service is shown as ‘Started’ does not conclude that everything is up and running. EngageOne installation guide suggests to check status manually after each service is started via http://<server>:<port>/status (e.g. http://localhost:8080/status). The page should load and display the system verifications. The same is true for each bundle, more details regarding system status check can be found in Server Status and Health Check Endpoint appendix.
EngageOne only becomes available when system check returns that everything is correct.
ResolutionUPDATED: June 7, 2017
In case this delay is of concern, patch is available on top of 4.3 GA. Additionally this fix is also incorporated in 4.4.2 and higher releases of EngageOne.