[KevinH]

I have literally worked editing for hours on many ebooks and have never seen that kind of sluggishness or memory usage and I leave Preview open constantly. But this is on macOS. I have been given one epub to test with that uses many svg image files that does seem to eat memory. But that is a known issue in the latest versions of QtWebkit.

So does your epub have svg image files inside its Images folder?

Does your epub have embedded fonts which seems to cause fontcache leaks on *some* Windows machines?

Are you using a particular feature of Sigil repeatedly that might help us reproduce the issue? Things like Regular Expression Search and Replace, Spellchecking repeatedly, running Reports repeatedly, Using Clips repeatedly, splitting or merging of html files repeatedly, etc? Anything at all that we might try to see if we can reproduce what you are seeing.

Also you might want to ask DiapDealer about trying his AppVeyor automated build of the current master to see if any of the fixes in there actually help (which would explain why we can not recreate the issues).

Please note DiapDealer is not experiencing any of these issues on any of his Windows machines after heavy usage of Sigil. This problem only hits some specific Windows machines and not macOS and not Linux, which is why we think it is a Windows 10 specific issue/bug.

A set of detailed steps to recreate this sluggishness/extreme memory usage with a public test epub (such as our own User's guide) would be really helpful in tracking down if this is a Windows10 issues or something else.