N:N subgrid, record created but dont appear

Hi everyone. I created an entity. Then I created a N:N Relationship between custom entity and account. I added a subgrid in the account form. When I created a record from the subgrid, the record Is created, but not Associated to the account record. The view of the subgrid Is not the problesm (it's filter). I momently see the record in the subgrid but it then disappear. Someone has an idea why the record Is created but not Associated? Thanks