SQL Server hangs on index rebuild, works well after SQL service restart We have a SQL Server 2014 enterprise cluster. Server 1 and Server 2.
SQL Server is limited to 64GB of memory.

We are using Ola Hallengren scripts for index rebuilding and optimizations once per week for all our databases.

Every time script triggers, it sometimes hangs on the same index 

ALTER INDEX [SecretId] ON [someDB].[dbo].[Articles] REBUILD WITH (SORT_IN_TEMPDB = OFF, ONLINE = ON)


This is unique identifier field in the database. Table has approx 1.5 mil records.

When index rebuild hangs, we do a failover to another SQL server, restart service on first one, and failover back to instance one. After that, we re-run scripts for index rebuilding, and it passes well in a matter of minutes.

Why do we need to restart service in order to rebuild index successfully?
I've come across this issue recently. In my case, Paul Williams' comment was spot on and it's to do with a complex nvarchar(max) column I had that stores JSON and HTML:

Is this a table with a large varbinary or nvarchar(max) column?  I've seen unusual maintenance behaviors with these kinds tables.

I use the following query to narrow it down to the offending table, which is a slight variation to Ola's script at https://ola.hallengren.com/scripts/misc/CommandLogSelect.sql
The index with a null EndTime is where the crash is occurring, most likely in the last row returned.
use [master];
SELECT DatabaseName,
       SchemaName,
       ObjectName,
       CASE WHEN ObjectType = 'U' THEN 'USER_TABLE' WHEN ObjectType = 'V' THEN 'VIEW' END AS ObjectType,
       IndexName,
       CASE WHEN IndexType = 1 THEN 'CLUSTERED' WHEN IndexType = 2 THEN 'NONCLUSTERED' WHEN IndexType = 3 THEN 'XML' WHEN IndexType = 4 THEN 'SPATIAL' END AS IndexType,
       PartitionNumber,
       ExtendedInfo.value('(ExtendedInfo/PageCount)[1]','int') AS [PageCount],
       ExtendedInfo.value('(ExtendedInfo/Fragmentation)[1]','float') AS Fragmentation,
       CommandType,
       Command,
       StartTime,
       EndTime,
       DATEDIFF(ss,StartTime, (CASE WHEN EndTime IS NULL THEN StartTime ELSE EndTime END)) AS Duration,
       ErrorNumber,
       ErrorMessage
FROM dbo.CommandLog
WHERE CommandType = 'ALTER_INDEX'
ORDER BY StartTime ASC;