No. In fact, in that topic the first image (jpeg from Wikimedia Commons) is successfully copied locally and displayed while the other two (png from our Discourse) are not. See https://discuss-space.wmflabs.org/t/new-advanced-mobile-contribution-features-coming-to-mobile/437
I wonder whether file format, image size or file size have anything to do with this problem. png’s are allowed in our instance. We are running v2.4.0.beta1 +50.