Seems some of your third-party plugins is not compatible with latest Roundcube release?

I manage 2 iRedmail/Admin-Pro servers, upgrade with the same procedure to 1.6.6. Including upgrade to Roundcube 1.6.4.

I upgraded Roundcube by copying the files to /opt/www/roundcubemail-1.6.4, then copying skins/plugins and the config.inc.php file from the old version. Moved the symbolic link to the new directory. It now looks like this:
          roundcubemail -> roundcubemail-1.6.4/
          roundcubemail-1.5.2
          roundcubemail-1.6.4

On the one server Roundcube works as expected, login with username password and access to mailbox.

The other server shows the Roundcube login as attached screen shot. In addition to username password it asks for server. I tried: 127.0.0.1, it then seems to login but to an empty mailbox.

I ran a diff between the Roundcube config.inc.php of the both servers:

4c4,6
< $config['db_dsnw'] = 'pgsql://roundcube:secred_for_server_1@127.0.0.1:5432/roundcubemail';
---
> $config['db_dsnw'] = 'pgsql://roundcube:secred_for_server_2@127.0.0.1:5432/roundcubemail';
> $config['product_name'] = 'HeuvelTop Webmail';
> //$config['skin_logo'] = '...';
46c48
< $config['des_key'] = 'des_secred_for_server_1';
---
> $config['des_key'] = 'des_secred_for_server_2';
49c51
< //$config['username_domain'] = 'xxxx.nl';
---
> //$config['username_domain'] = 'yyyy.nl';

Searching for this issue I found one message related relating to a very old version of Roundcube.

What to do next?