I had this same trouble with Prizrak not dying, but hotfix and restart corrected it.
Now Im having trouble with ending the mission. I have all the tasks completed except the 'Find evidence' part which is 1/2. Do I need to find evidence somewhere to end the mission? I'd like to progress without using 'endmission' or other workarounds.
Also, someone mentioned the optional missions, I have played this mission three times to Prizrak point and I've never seen any side missions. Yesterday I found the group with BMP-2 and couple of UAZ loitering around, but havent got that as mission.