This issue concerns the plugin API of Form2Content 6.17.4 (Joomla 3.9.3).
The onAfterF2cContentSave event handling method receives a F2cEventArgs parameter. The contents of that object is rather illogical and counterintuitive. Let me explain using the title:
$args->formNew->title contains the text for the title of the field. However, $args->fields->title->values and $args->fieldsNew->title->values are empty. This is not the case for custom (non standard Joomla! article) fields. For those fields the values array contains the entries for the associated field.
Why dis discrepancy? Why do $args->fields->title->values and $args->fieldsNew->title->values not contain the value of the title field?
Pieter-Jan de Vries
Questions and answers for Form2Content, a Joomla CCK.