Assume that you use SQL Server 2017. When you delete an attribute which contains customer index from one entity, you may notice that the index records in "mdm.tblIndex" for the other entity will also be deleted if it has the same "SysIndex_ID".
Microsoft has confirmed that this is a problem in the Microsoft products that are listed in the "Applies to" section.
This issue is fixed in the following cumulative update for SQL Server:
About cumulative updates for SQL Server:
Each new cumulative update for SQL Server contains all the hotfixes and all the security fixes that were included with the previous cumulative update. Check out the latest cumulative updates for SQL Server: