Typo in tform_base.inc.php
In the file interface/lib/classes/tform_base.inc.php there is a bug at line 1190, the ip_address index of the $sql_v6 table is not surrounded by quotes, it therefore passes for a non-existent variable and causes a warning as well as an incomplete display of the error.
https://forum.howtoforge.com/threads/bug-in-interface-lib-classes-tform_base-inc-php.91338/