What can I do with multi-subfigure figures on ResearchGate.net
One answer, hinted at by @Anyon's comment, is to generate, for each figure, a PDF with the subfigures laid out as they are in the full work - and upload that. Perhaps one also needs to include the subfigure captions in that PDF.

This seems like a lot of hassle, but perhaps one can make LaTeX automate this somehow.