TypeError: Cannot access offset of type array on array

On a webform submission we get this fatal error. It seems random as most submissions go through without issue.

Relevant PHP error trace:

TypeError: Cannot access offset of type array on array in /.../http/core/lib/Drupal/Core/Database/Query/Merge.php on line 331 #0 /var/www/vhosts/movu-robotics.com.d9/releases/2025-09-30-14-03-35/http/modules/contrib/cleantalk/src/CleantalkFuncs.php(681): Drupal\Core\Database\Query\Merge->key(Array)
#1 /.../http/modules/contrib/cleantalk/cleantalk.module(390): Drupal\cleantalk\CleantalkFuncs::_cleantalk_check_spam(Array, Array)
#2 [internal function]: cleantalk_validate_webform(Array, Object(Drupal\Core\Form\FormState))
#3 /.../http/modules/contrib/webform/src/WebformSubmissionForm.php(1906): call_user_func_array('cleantalk_valid...', Array)
#4 [internal function]: Drupal\webform\WebformSubmissionForm->validateForm(Array, Object(Drupal\Core\Form\FormState))