Even if they didn't glitch, they would be bored. The missions are so rubbish.
I thought the missions are getting better when you lvl up? or always the same stuff ? If so -.-
They always consist of the same stuff. I'm level 43 and I'm still doing the same missions I was when I was level 6. It's always "Get the coke/meth" or "kill that guy" or "blow that up". There are a handful of interesting ones but those are usually drowned out by the boring missions.