Nextcloud file has changed since discovery

Apache/2.4.25 (Debian)
PHP 7.0.30-0+deb9u1
Nextcloud 13
Debian 9.5
Nextcloud client 2.3.3 build 1

I get the following message on m nextcloud client, on windows 10. I tried to fix it by removing the folder sync connection and re-adding it. But the same messages appear.

What does this message mean, and how can I fix it?

Thanks

I have a user who encounters the same problem. He did not even change the listed files since he added them to nextcloud through the desktop client.

I don’t know if it is a real problem, but it is a bit scary to see strange (and seemingly not relevant) warnings for such a long list of files…