Flex container does not hide via dynamic attribute

[Teodor]

Please check Patricks reply here, regarding date values 00-00-0000:

How to update a NULL

Is there a default value set on that column in the database. The zero date is a special date from mysql and is not a valid date string. You can disable zero dates in mysql https://dev.mysql.com/doc/refman/5.7/en/sql-mode.html#sqlmode_no_zero_date. Also the expression for default null should be {{$_POST.data_modified.default(null)}}. A null value, not a string.