Migration SQL Source with Track Changes
I had an issue like you did and i solve it by changing my:
track_changes: true

on
  high_water_property:
    name: changed
    alias: n

But the problem with this way that you need to:

Manually delete, NOT update your database destination fields.
Import old data.(Before check your source plugin, it must have changed field!)
Update your database with new data.

(and only than high_water_property will work)

About this two Source Plugins
Declaring highwater property in Migrate
About track_changes