You rebuild a non-clustered index by using CREATE INDEX together with the DROP_EXISTING=ON and ONLINE=ON clauses to add a new column to that non-clustered index in SQL Server. If you add a new column to the nonclustered index, you may encounter blocking in a different SPID when write operations such as INSERT or DELETE are performed on the same underlying table during the index rebuild period.
This issue is fixed in the following cumulative updates for SQL Server:
Microsoft has confirmed that this is a problem in the Microsoft products that are listed in the "Applies to" section.
Article ID: 3194365 - Last Review: 2017 mar. 20 - Revision: 6