Windows client re-downloads everything, even though virtual files are enabled

I am seeing this on three desktop computers with Windows 11/10: The all suddenly insist on re-downloading everything in one synched directory of a particular host.
Unfortunately, this is a rather large directory with thousands of images: ~90 GB. Virtual files are enabled. Even after explicitly chosing “free disk space” in the properties dialogue, the client still insists on fully downloading everything. Has anyone seen this kind of behaviour? Is this likely a bug or something misconfigured on my server? I’ve checked recent activity on the server and there is very little, so there is definetly no reason to re-download everything and definitely no reason for a full sync.

Are you able to tell whether all of the misbehavior is associated with solely with one folder? Or does it just appear to be this folder because it’s the biggest/most obvious one?

If it is just this folder and no other folders are behaving this way, is there maybe something different about it versus the others?


Is it Shared?
It is on External Storage?
Is it a Groupfolder?
Is it Encrypted?

Not really. I found that suddenly, the creation date for all 30,000 files in that folder were changed to the current date. So what I did was to restore the last backup and have occ rescan the folder. I have no idea what triggered the change of the date, whether it was caused by one of the components of nextcloud or by the operating system or by whatever. And I have no idea how to narrow the culprit down. I guess, this will remain forever unsolved.