The ACP_COOKIE_SETTINGS_EXPLAIN key in board.php contains <b> which according to https://area51.phpbb.com/docs/dev/3.2.x/language/validation.html should not be used.

Says:

<b> should not be used, use <strong> instead.

    'ACP_COOKIE_SETTINGS_EXPLAIN'        => 'These details define the data used to send cookies to your users browsers. In most cases the default values for the cookie settings should be sufficient. If you do need to change any do so with care, incorrect settings can prevent users logging in. If you have problems with users staying logging in to your board, visit the <b><a href="https://www.phpbb.com/support/go/cookie-settings/">phpBB.com Knowledge Base - Fixing incorrect cookie settings</a></b>.',

So i guess change:

<b><a href="https://www.phpbb.com/support/go/cookie-settings/">phpBB.com Knowledge Base - Fixing incorrect cookie settings</a></b>

To:

<strong><a href="https://www.phpbb.com/support/go/cookie-settings/">phpBB.com Knowledge Base - Fixing incorrect cookie settings</a></strong>