I have seen these errors and have done a little research that might shed some light on the subject. Not much in solving them but may lead you down a different path.

Unfortunately the only conclusion that I could come up is that the routing engine thinks that I-85 Bus is quicker than taking I-85. I can not conclusively prove this as the data I have used below shows it to be to the contrary plus supposedly Waze speed data is more granular than what we have access to as well.

Here is the data I have come up with:

The section between the two I-85 business interchanges is the following:
I-85 Bus - 8.1 miles
I-85 - 8.91 miles

Time to travel between those segments (this is using tools for the speed data, the best we have access to and maybe even erroneous)

I-85 Bus - 8.53 minutes
I-85 - 7.3 minutes

So I-85 Bus is shorter but longer time wise. I just can't find any start/stop combo that forces to use I-85 as the "primary" route. It will show up in the secondary routes you will obtain.

I think you just need to chalk this up to unsolvable at the moment. Unless I missed something and someone else chimes in with a good reason. I have a sneaking suspicion since the route is shorter that may be a factor but can not prove or disprove that theory.

Well yes you will probably get some weird results from shortest but the point I was trying to make is that for some reason the routing engine is triggering taking the shortest route whether or not it is the quickest. Just a theory mind you that is based in my head and I can't prove it.

You bring up a good point. I have at times switched my routing style to shortest path and it seems to do worse than the fastest route. This is because shortest routes take me down some weird less traveled roads which I simply don't want to travel on so I decide to go Y rather than X.

I'm guessing this is what is happening. That the users have changed their routing styles or are there by default and don't know which style they are routing on.

Although the same can be said about the fastest routing method in that this too might also take me down some weird streets when a main street is perfectly fine, and usually preferred, than say down a residential street or the like.

I'll probably do some driving around the area and see what happens with the routing styles later today.

Moved to US forums for research and discussion.

Once the editor behaves a little better for me, I'll see if I can find anything.

I just tried the livemap to route from before to after the split....

Option 1: I-85 N, 9 min, 11 miles
Option 2: I-85 Bus N, 10 min, 10.5 miles

And the reverse:

Option 1: I-85 S, 10 min, 11.5 miles
Option 2: I-85 Bus S, 10 min, 11 miles

I was hoping to get the Business route on top to then try the beta routing engine, but oh well.