@ Dentite
My Yugo Tok also has your trigger symptoms. Sometimes it works fine; sometimes it won't budge no matter how hard I pull. Usually, it goes bad when it is hot...after firing a mag or two. Also, I can tell when it goes bad...the reset feels off and then when I try to pull, the trigger feels like the mag safety is engaged (i.e., like how the trigger feels when the mag is out). At first, this made me think the mag was moving around in the grip, but then I looked at the safety.
I could see the trigger group had removed some of the bluing on a small area on the right side of the safety; there should be no rub there as that is the part of the safety that is out of the way and allows the trigger group to move freely. This told me that part of the safety was touching the trigger group when the safety was disengaged. I then checked the position of the safety and it appeared the installation holes were not drilled perpendicularly through the frame. More specifically, the right side hole was drilled slightly forward of the left side hole. So, this poor installation was causing the safety to touch the trigger group even when the safety was disengaged. I confirmed this all by firing the gun with safety installed until the trigger failed, then quickly removing the safety from the pistol (the trigger worked fine for multiple mags), and then reinstalling the safety until the trigger soon failed again.
Since then, I have been slowly filing the rubbed area on the safety every time the trigger fails at the range. One day, I think I will have removed enough material that the trigger works fine with the safety installed. If not, I'll just remove the safety permanently.