Linking to other knowledge base articles sometimes doesn't convert from Markdown.
Its a glitch in our editor rules will be addressing this in upcoming release.
Just realized what's going on. When I copy the link from another article and then paste it in the link input field, for some reason, a space is added between the / and the article slug. You can see it in the GIF. I am not adding this. I'm simply copying from another article and pasting it as is in the link modal.