To date, there have been no experimentally observed deviations from quantum mechanical predictions in well-controlled and verified experiments. Quantum mechanics has been extraordinarily successful in describing a vast array of physical phenomena, and its predictions have been confirmed to an incredibly high degree of precision.
However, it is important to note that there are still open questions and areas of active research within quantum mechanics itself. For instance, the nature of quantum gravity and the unification of quantum mechanics with general relativity remain unsolved problems. Additionally, certain aspects of quantum mechanics, such as the measurement problem and the interpretation of wave function collapse, continue to be topics of debate among physicists.
While no experimental deviations from quantum mechanics have been observed thus far, it is always possible that future experiments or developments in theoretical physics may lead to the discovery of new physical models or modifications to our current understanding. Scientific progress often involves refining existing theories or proposing new ones when inconsistencies or limitations are uncovered. However, any new models or modifications would need to account for all the existing experimental successes of quantum mechanics while also providing testable predictions that differ from quantum mechanics in specific scenarios.