Rabbi Haim Amsalem has written and lectured extensively about the annulment or non-recognition of conversions done by Orthodox rabbis who are not under the authority of Israel's Chief Rabbinate. The scandal, of course, is not just in Israel, but throughout the diaspora. An authoritarian group of rabbis claims exclusive authority to recognize halakhic conversions, and in the process they both violate the halakha egregiously and cast aspersions on fine halakhic converts. The sin of oppressing converts is among the most serious in Jewish law. Please read Rabbi Amsalem's article: https://www.jewishideas.org/article/conversion-scandal