@baris
Was able to pinpoint why the pngs weren't uploading. Its because the filename was using scandinavian letters, ÅÄÖ in it. If I remove them it works.

This is still working pretty well to upload basically any fileype. This on a git clone from last night.
Having "Allow users to upload regular files"(having no effect turning this on or off) unchecked and using the upload image from the imgur plugin as the uploader. It only gets uploaded to imgur if it's a .jpg file, all else gets uploaded locally.

Also, .png files gets uploaded locally as well, but afterwards the url isn't replaced, but it says (uploaded 100%) after the filename.
Above works the same here on this nodebb installation.

examples below:
output.log