If the claimed invention lacks reproducibility, this may become relevant under the requirements of sufficiency of disclosure or inventive step. The technical effect achieved by the invention solves the problem which underlies the application. If an invention lacks reproducibility because its desired technical effect as expressed in the claim is not achieved, this results in a lack of sufficient disclosure, which has to be objected to under Art. 83. Otherwise, i.e. if the effect is not expressed in the claim but is part of the problem to be solved, there is a problem of inventive step (see G 1/03, Reasons 2.5.2, T 1079/08, T 1319/10, T 5/06 and T 380/05).
See F‑III, 3 for cases where successful performance of the invention is inherently impossible because it would be contrary to the well-established laws of physics.