I've seen this on several highways in the UK.
It's an error in the mapping data that makes the routing algorithm think that going down the off slip road and straight back up the on slip road is both shorter and quicker.
I've even had it tell me to drive through a layby (rest stop) instead of staying on the road!
For those of you in the UK - it happens every time I go west on the A303 near Thruxton, and east on the A30 just west of Basingstoke.