Simply extruding from the street did not work for me.
What I ended up doing was shift-d copying the curb object, then selecting the street, then joining the two objects. I thought that’s what I did the first time.
That fixed the issue for me, but I’m not certain why it was broken in the first place. Knowing why would be good for me, and maybe others, and would allow someone to correct the issue if they didn’t have an object that wasn’t broken.
