When we remove a table or add a loose table the collection does not get set dirty which means the change is never saved.
More info here https://forum.unity.com/threads/english-column-disappearing-automatically.932532/#post-6101337

1) Create a new string table collection with 1 or more tables in it.
2) Save the project
3) Select the table collection and remove one of the tables. Save the project.
4) Restart Unity.
5) Select the table collection, notice the table has not been removed.