OOF I feel this @_@ similar but different:
earlier this year I commissioned someone to make a video trailer for my comic, and when I sent them the panels I wanted to be used they're like "oh hey, I can't use any of these ones from page like 1-5, they're too low resolution."
"What? They should be the same as the others. Let me see what's up."
Well what was up is that those first several pages my workflow was still a little shakey, and I had accidentally saved the master versions of those files at the 940 pixel wide size instead of just the pngs. LUCKILY doing traditional linework came in handy, still had the scanned versions of it at full size, so was able to just quickly recolor those pages for the video. But been extra anal about how I save afterwards...