Yeah, I got the same issue. Actually, the mission flow is a bit confusing. After taking off and when on route to NDB 525, ground says enemy aircraft in the air and then pursue them though I could not see them at all and they are pretty far away so there is no way to catch up with those enemy Mig-19s. So the confusing part is should I keep going to NDB or follow them.. actually the only way to do it is to use F10-Map which is kind of cheating to me. In any way I got though I got hit by SAM. However, I did read that S75 can hit only above 3km high so I went low (below 1km) with 6th group and managed to fly close to Tbilisi airfields which are the mission goal. Although, the mission trigger did not work out so mission has not been accomplished.
I'm wondering if the mission needs to be update to a newer version of DCS or something.