The motorway junction thing seemed unlikely to me too, but it seems to have worked! The only other change I made was trying to change the segments so the offramp came off at the end of a motorway segment and not at a point along it, but I didn’t do that for the southern (second link in the original post) offramp.
Anyway, when looking for other examples in my processed data I found another example in Melbourne (linked below). Using a Geofabrik extract downloaded on March 16th there was a very similar routing error where vehicles would be routed off the Monash freeway, take Waverly road and then rejoin the freeway. As you can see in the link it’s fine now. The relevant nodes here are also marked as motorway junctions, but I can’t find a record of them being changed in the past 5 weeks or so.
https://www.openstreetmap.org/directions?engine=osrm_car&route=-37.8789%2C145.0839%3B-37.8865%2C145.1085
