Actually you need to do add the correct mapping configurations[1] in the registry.xml file in wso2 esb.
[1]
<mount path="/_system/governance" overwrite="true">
<instanceId>reggov</instanceId>
<targetPath>/_system/governance</targetPath>
</mount>
Remember if you mapped governance to governance as configuration[1] the rest of the collection comes under the target path(/_system/governance) will not be appeared.
Ex:The following mapping[2] will not make sense with the mapping [1].
[2]
<mount path="/_system/governance/abc" overwrite="true">
<instanceId>reggov</instanceId>
<targetPath>/_system/governance/xyz</targetPath>
</mount>
The real cause for your issue can be, the registry caching time of the ESB.
Based on the current implementation it takes around 15 minutes for an artifact deployed to the GREG to be synched to the ESB nodes. The reason should be the default cacheable time is set to 15 minutes.