save_size=1000000 I'm not sure if I want to increase the default save_size by 10x, but if, say, 200000 (2x) or 3x is enough, I could change the default. Can you give that a try?
After all, it happens for you on some large document, more than likely it will happen to other people with their own large documents. And if it's L3-related (not surprising), becomes even more likely, even independent of tex4ht. --thanks, karl.
