CSRF checked filed

There are many posts related to CSRF checked filed however no post helps me.

Our Nextcloud is version19.0.4 .

We use it for file sharing among the team with out login authentication. just sharing folder with password for editing.

One of the member reports that there is the message ‘CSRF checked failed’ once in the morning when he starts his work.
Then, soon he can access to the folder normally and there haven’t been the message during the working time.

I can’t find any error message in the log .I need some hint to solve the problem.