[dginev]

For the image widths, there is some CSS fine-tuning that is still needed on the arXiv HTML side. I think that will get fixed soon, just needs the right height directive set.

Getting subfigures emulated via flexbox is one of our more recent LaTeXML enhancements, and still has some ongoing work (working on it today actually). It can be a bit finicky to test - there are easily 20 different ways people can write LaTeX for subfigures in arXiv.