It seems the upload issue might have been caused by a mismatch between the file type and extension — for example, if a PNG image was being uploaded under a .svg filename, the system would throw an error.
In any case, I’ve uploaded both updated diagrams as new versions of the previous files. I’ve added myself and andygol to the list of authors for helpful feedback, software tips, and the idea to improve diagrams with accessible colors.
Many thanks to everyone who took part in the discussion!
https://wiki.openstreetmap.org/wiki/File:Railway-station-tagging.svg
https://wiki.openstreetmap.org/wiki/File:Railway-station-tagging_simple.svg