Deadlock-like in Compute Engine on SQLServer

Context

Views computation, SonarQube running on Windows with an MSSQL database, multiple CE workers

Symptom

Background Task never ends. It 'freezes' just before the last log (the one saying ' Executed task ' ). Only a server restart can unblock the worker.

Local setup

reproduced on both 5.6.3 (Governance 1.1) and 6.2-RC1 (Governance 2.0.0.1580).
MSSQL v11 (SQL Server 2012) . Customers had 2012 and 2014.
12 CE workers .
3 projects, one view per project + one master view

Important observation

Bug is reproduced locally only if querying the Background Tasks page (in the Web UI) immediately after the Views tasks were submitted to the server. If no query in the UI for a minute, then refresh the UI only later on, Background Tasks show as successfully completed.

Initial investigation

VisualVM: no thread locked
Database: tasks are stuck in ce_queue and are not in ce_activity