Models struggle in 2 main areas. The first is spatial reasoning: often the models make off-by-one errors which they find it hard to recover from (as factories are very sensitive to these mistakes - like in programming). The second is in long-term planning, i.e figuring out what to do strategically, before making tactical subgoals.

The difficulty scales in lab-play generally in proportion to the depth of the production chains. If an item requires several factory segments first, this makes it a lot more challenging. I think this is related to planning though, as the models tend to get down 'into the weeds' of fixing minor issues - rather than coming up with a master plan first.