Getting this error out of sudden: apparently the only thing changed was "CRM/Core/Payment.php" file moved to the custom php directory and a "City" field attribute changed to "not required"
API error: 'afform_type' is not a valid option for field option_group_id on OptionValue.create( entity name form)"
Indeed, 'option_group_id' in the civicrm_option_value table is of type INT, while new record creation API call looks like this:
[id] => 1303
[is_active] => 1
[option_group_id] => afform_type
[name] => form
[value] => form
[label] => Submission Form
[weight] => 0
[icon] => fa-list-alt
[version] => 3
This is clearly broken but I have not a slightest clue why: nothing has been changed since yesterday.