I did a search already and found another person having a similar issue to mine, however I don't have access to the mission prior to this one, I know I completed it 1/1 times (when it was first introduced it only needed one completion) then I also know it was changed, but I can't see it in my missions, and I can't do the other one without it...

There must be some mission before it that you didn't do. Follow the mission chain on the wiki to see which of the missions you have available that you haven't completed: http://galaxylegion.com/wiki/index.php/ ... z_Incident

I made the mistake of thinking the Glaviz Incident was directly before the Glaviz Vendetta, however there are two Zolazin missions in between (Zolazin Pursuit then Zolazin Battle). Both of which I must have done 1 completion of as they were weekly, however I only see the Zolazin Pursuit. Well confusion over, and thank you!