I'm in a similar position. Every thing else is done. Speznas attack when droping off Lopotev, all Vills are Blue/Green. Only Investigate the location (Small island to South East): which i can't seem to find anything at night.
So I left for the Russian encampment. Tried "nice". Then "nasty" then insurgence. Placing a stealthy sachel near every Bird and set of wheels gets me seen eventually. Clearing a hanger of what looks like flight crews that nave no NVG's sets off the alarm. Blowing the sachels fails the mission. finishing the overall mission. Only to bring you to a new level that's called "revelations". The revelation is that i'd just actuated a nuclear responce from the Russians......
DOH! Time to wait for day break then "investigate loacation" again i guess......