Versioned relational records will be duplicated when a many-to-many formcontrol picker is saved. This happens if a relational object is versioned.
This is the versioned relational DB table when the duplicate first appear, generated during save:
The select query for many-to-many formcontrol is such
The generated fromcontrol tagging is
A temporary solution now is to delete duplicate tagging from the many-to-many form control manually before submitting the form (if they appear).