Okay this is actually the same issue as I wrote in this post a while ago but now I actually figured out what specifically it is.

Looks like when a user uploads an image post, there is no “source”, so where a URL is supposed to go (like in that first post in the screenshot) there is nothing. For a self-text post, it looks like that’s accounted for in the code, but for self-image posts it’s not, causing double dots.

Image-self posts that don’t have a source URL should only have one dot, just like self-text posts.