@ Davo Hmm .. which direction you can not connect? because it worked on me in all directions. Always place the interchange independently (without snapping to existing highway), and then you can build a connection from the existing highway to the interchange using the highway road. i hope it works for you. btw thanks for reporting it

I've found it's impossible to connect it to the existing motorway because the lanes are too close together. Is there some way around this that I'm not seeing?