Complex Langevin simulations allow numerical studies of theories that exhibit a sign problem, such as QCD, and are thereby potentially suitable to determine the QCD phase diagram from first principles. Here we study QCD in the limit of heavy quarks for a wide range of temperatures and chemical potentials. Our results include an analysis of the adaptive gauge cooling technique, which prevents large excursions into the non-compact directions of the SL(3, ℂ) manifold. We find that such excursions may appear spontaneously and change the statistical distribution of physical observables, which leads to disagreement with known results. Results whose excursions are sufficiently small are used to map the boundary line between confined and deconfined quark phases.