After upgrade : False conflicted copy, files re-upload after delete


With my two last upgrade of Nextcloud (25 → 26, 26 → 27), we have experienced some real issues in shared folder : some sync desktop clients reupload deleted files, or people have a lot of false-positive conflicted copies.

Do some people experience the same issues ?
How investigate this problem ?

Some times sync clients are not up to date but it does seems to be the core of this issue.

thanks in advance for your help