[KevinH]

Does it matter if you are moving to a new tab (just created since it was never open before) or must it be an old tab (previously open but not the active tab)?

Given you said it takes days of active use to see this, my guess is a memory leak or broken event/signal delivery. I have tested for memory leaks in Sigil under macOS and Linux and did not find any.

Google reported a bad Windows 10 memory leak for pages allocated for javascript/jit used in Chrome. Not ever sure if Windows ever fixed it. Google tried to work around it by caching and reusing pages but that version of chrome only made it into Qt 5.15 and later versions.

The only other solution was to periodically shutdown chrome/Sigil and restart or even restart Windows 10. Again this takes days and days of active use without quitting Sigil to see at all.

So very few people ever run into this problem and only if they have a work flow that never restarts Sigil over days and days.