SQL query keeps blocking all the others

Hello,
One of our clients is using JIRA 6 and DVCS 1.3.1.1. Recently, we've been having stability issues with the DVCS plugin.
Basically, here is what is happening:
1. DVCS generates a SQL Query on the database
2. This query, for some reason, gets "stuck" and therefore blocks all the following queries
3. This makes the DB Connection Pool quickly full and eventually JIRA crashes.

Since I've deactivated DVCS the issue didn't happen again, that is why I believe the root-cause is the DVCS plugin. The SQL query that always blocks all the others is the following:

SELECT * FROM jiraschema.AO_E8B6CC_CHANGESET_MAPPING WHERE SMARTCOMMIT_AVAILABLE =  @P0   ORDER BY DATE DESC

We are using JIRA 6.0.3 and DVCS 1.3.1.1 and SQL Server 10.50.4000 database.

Can you please let me know how this can be fixed?
Also, I wanted to upgrade to 1.4.0.1 to see if it would fix the issue, but I cannot do that because of DCON-330.

Thanks for your help,