Hi again @asmecher,
I think it’s solved already. By querying the table controlled_vocab_entry_settings, we found lots of null values for column setting_value.
A big batch of back issues had been inserted with QuickSubmit, which treats keywords in a different manner as far as obligation of insertion is concerned.
We queried the db so as null values where replaced with a sample word. That solved the issue.
Regards,
Juan