(I think this is an old bug, not just with the new version, and I don't remember if it's been filed:)

When uploading an image (or a cart?) to the BBS with the file chooser, if the filename contains spaces, the upload will appear to succeed, but the file will not appear in the image list. For example, when I take a screenshot on macOS, the file with the original filename of "Screen Shot 2017-12-13 at 11.08.48 PM.png" will exhibit this behavior, but if I rename it to "screenshot.png" and upload it, it works as intended.