PMA - An error occurred while authentication!

I still have this problem with all my systems migrated from ispcp:
If a user logged in and click PMA links:

I have already checked for old IP addresses in /var/cache/bind
but did not found any IP conflict ...

need help

more details:
using external NS
i found out that there is a difference in /var/cache/bind/admin.host3.domain.tld.db
between a test installation in V-Box and real server ...
at the end of the V-Box file I see many entrys like:

/var/cache/bind/admin.host3.domain.tld.db real server shows only one entry at the end:

do you think it is possible to delete and re-create all the BIND files by running an update and how should I proceed?

found out a bit more ...
I have protected /var/www/imscp/gui/public with .htaccess
is there a way to get it working with PMA session and .htaccess?

this htaccess should work but it's also blocking:

I had bruteforce attacks from a botnet for about 2 months ... which means blocking of IP addresses did not helped
the only way to stop the attacks was using additional htaccess password protection

I have tried another solution with a cookie check and redirect to panel login ...
the User have to login first before using PMA

could it be that mod_rewrite is not working within the /tools folders?
the cookie has been set but I guess rewrite (second htaccess) did not work
fex:

but fail2ban is useless because recently a attacker is using IP pools from a botnet ...
I have watched this many times ... the same IP will be used only one time and afterwards a new attack with a new IP is started
no way to block this kind of attacks with iptables or whatever ...
that is why PMA and Filemanager should be protected with a captcha or used only within the controlpanel