I am having same prob, Snagit stops after 1.8 min. To be more specific, I recorded for around five minutes and then hit stop. But when I try to play it back it stops when the moving cursor (whatever you call that indicator on a line moving along as the video plays) and when that indicator gets to the end of the line (only .30 seconds or 1.8 minutes on two different attempts) it just stops. I have no way to see/hear my recording beyond that point.
I fixed this problem by sending app to the trash and then reinstalling. Then problem vanished. So I guess one can get a bad installation.
Then, when I tried to edit the video I was puzzled because I saw no editing features not realising you just needed to double click on the sliders which causes a pop up window to appear with a "cut" option. It wasn't until I watched a tutorial on editing that I saw you need to spread out the sliders with start cut and stop cut indicators spread apart from one another and then click on cut.