Possible causes are as follows:

Hive/HBase components were not selected during MRS cluster creation.
The network between the CDM cluster and MRS cluster was disconnected when an MRS data connection is created.
The CDM cluster functions as a network agent. MRS data connections that you are going to create need to communicate with CDM.

Why Are MRS Hive/HBase Clusters Not Displayed on the Page for Creating Data Connections?