Log error when a TranslatableMarkup is created with a non-string input

After some modifications in my block settings and my custom menu which are all migrated from a drupal 6 site i got the following error on blocks layout page:

InvalidArgumentException: $string ("Array") must be a string. in Drupal\Core\StringTranslation\TranslatableMarkup->__construct() (line 140 of core\lib\Drupal\Core\StringTranslation\TranslatableMarkup.php).

Perhaps the issue is not related to the block modification but after uninstall blocks module the error disappeared.

This is a translated one lingual Hungarian site running on Drupal 8.1.0.

Please help! I am really stuck :(