I have this problem now and I can’t find any reason for it. My slugs are all right, with one two-word exception (“Sale Pending” is slugged as sale-pending). I tried making both the title and slug one word and that did not fix it, even when I restarted. So I put it back, as this server is in production.
I also took off all my custom pins and icons, and restarted, and it still doesn’t work. Putting back some custom pins now since it’s again in production and looking messy with missing icons.