Complex sentence: A case could languish for years in the OVIR (ОВиР) department of the MVD, an often cited but rarely explained official ground for refusal to issue emigration visa were "national security reasons".
Split into simpler sentences: A case could languish for years in the OVIR (ОВиР) department of the MVD. An often-cited but rarely explained official ground for a refusal to issue an emigration visa were "national security reasons".