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[patrik69]

Thanks a lot for the help, I should have thought of that before.

I have another small problem, which existed before the update of the style of the forum.

Sometimes, users find themselves logged in with another user's name, but luckily they can't post.

How to correct this problem?

Thanks in advance.

[axew3]

Sometimes, users find themselves logged in with another user's name, but luckily they can't post

It is not possible.

This is a WP plugin, and nor using the phpBB extension it can be possible (because it just update email and pass and url in wp when updated in phpBB).
So something goes wrong on pairing emails between phpBB and WP?

Since it is an integration by email, it is possible to have an user with an username in phpBB, and another in WP with the same, but different username. So may it is the case?

Note that you should only allow users to update their email and pass and register only in phpBB or WP if not using the phpBB integration extension.
Note also that you should check for users with duplicated emails in phpBB, and setup phpBB to NOT allow email reuse for different accounts!
You can check for duplicated emails with a click into
List phpBB users with duplicated usernames or emails
on Wp w3all Check admin page