Some users unable to login

Hello
I have an issue that appeared without having changed anything (nothing obvious at least):
some users are unable to login the admin page (after the login page they are redirected to the main page of the website), however I can without issue
I tried the following:

• resetting the password for existing users
• creating a new user to test, same issue
• updated WP to the latest version
• deactivating all plugins
• deactivating the theme
• activating the debug but there is no error appearing
• I had a look at the database but saw nothing obviously wrong in wp_users and wp_usermeta

I ran out of ideas on how to fix this, does anybody have any?
thanks a lot

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