From my own experience, i would say incomplete requirements will always hinder the successful delivery of the project.
So back in 2022 I was working as software tester on application which has stripe payment gateway integration and real time payment status updation for payment/refund.
The project started on good note however later on the client realizes somehow that documentation was not properly maintained. And taking advantages of that they start giving so many changes in the requirements that the subsequent sprints become completely mess.
Not all the clients are same, but our bad luck was that the project was already lengthy and on top of that we met a client who had such thought, all this made the project completely mess.
The worse thing if the documentation is not maintained and project turned out to be failure then BA or PM are usually the first person to face the consequences then later on all other team members.
In my perspective I would suggest to have clarity on requirements, taking sign-off for the requirements is necessary else it will difficult to decide the exit criteria for the sprints.
In some organization there is no BA or PM and qa have to handle it, then still same approach should be preferred that requirements should be cleared, else we cannot visualize the product for testing that we are about to deliver.