I really hope what I have helps. Been trying to figure this bug out for a while now. From what I can tell, it has alot to do with loading terrain and or geometry (e.g.Tanoa). Looks to me like it can also be accelerated by jumping around maps alot, like teleporting or flying jets. Fixed wing showcase is a good contender.

So, I have done some looking around, and found that there is always a steam authentication failure when trying to join a headless client to a local client over the internet, even when on the same network, which undermines half of the point in my opinion. I'm also not planning on buying a second copy of ArmA, so there is a bit of a hiccup. The whole system works extremely well, except for this.