Persistent Severity 016 alerts: "Change Tracking autocleanup is blocked on side table"

We had a large database running on a SQL Server 2014 Enterprise instance (evaluation license). Due to cost constraints, we had to move it to a new SQL Server 2017 Standard instance (per-core license; just updated to CU6). **EDIT: The database is in SQL Server 2014 (120) compatibility, and was transferred by restoring full and log backups.** Everything is working fine except for change tracking. We use change tracking to locate recent changes and keep a denormalized table up to date; the denorm table is used for rapid filling of a grid for the web application. Change tracking is working, but apparently autocleanup is not. We are getting Severity 016 alerts: > Change Tracking autocleanup is blocked on side table of tablename. If the failure persists, check if the table tablename is blocked by any process. These come about every half hour for each of the tables that is complaining (about 4 different tables). We've tried the manual cleanup described [here](https://github.com/Microsoft/tigertoolbox/blob/master/change-tracking/ChangeTrackingCleanup.sql) ... it too presents "side table is blocked" errors. So here are my choices: 1. Turn off this specific alert and hope nothing blows up. 1. Turn off autocleanup; schedule a manual cleanup during a daily maintenance window. 1. Not sure what else I can do. Besides "what should I do to stop this?", my side question is "why is this happening with 2017 Std when it didn't happen with 2014 Enterprise?"