You started your node when a lot of synthetic test data was being added to the network… as part of getting ready for new/large customers. That explains the fast growth (as normally it would take you a year+ to receive 10TB).
Recently some improvements have been made to the deletion of old data (some of it was missed before: and should have been deleted weeks earlier) … and test data has been paused to allow some of those new customers to begin their own performance testing.
So you’re seeing the same thing as the rest of us: lots space being freed up recently. Nothing to worry about!