Forwarding a message @garnacho sent to distributor-list about a recent Tracker bug. If you use a bleeding-edge distro and you recently saw performance problems appear in Tracker Miner FS 3, check for updates.
The latest SQLite releases (3.35.0 and 3.35.1) are known to break Tracker 3.x . The issue has been communicated to the SQLite developers and a fix is already available  and scheduled for SQLite 3.35.2. In the meantime I advise to avoid mixing these SQLite releases
with Tracker 3.x, or backport the SQLite fix.