Well, that sure is annoying. Tried to replicate the bug by downloading OperaGX myself. Seems to work without a hitch on my largest savefiles. Also could not find any specific developer question related to OperaGX file storage. For now I am out of things to try, if the problem persists, all I can recommend is using a different browser. Thanks for reposting the issue! Sorry I can't find a fix for you right now, maybe something will come up in the future that explains the problems