Changes are lost when collapsing a paragraphs subform including an inline_entity_form

@heddn can you elaborate on the regression you mentioned in the reverted #2901158: Changes are lost when collapsing a paragraphs subform including an inline_entity_form →

This commit caused regressions with non paragraph IEF fields. I have an (albiet complex) IEF implementation for user that completely broke after this commit. Any chance this could see a revert while a test coverage and fixes are added?

I guess we need a test for this, otherwise this issue is going nowhere.

#9 causes error with Paragraph:

TypeError: Drupal\Component\Utility\NestedArray::getValue(): Argument #2 ($parents) must be of type array, null given, called in /var/www/html/web/modules/contrib/paragraphs/src/Plugin/Field/FieldWidget/InlineParagraphsWidget.php on line 1320 in Drupal\Component\Utility\NestedArray::getValue() (line 69 of core/lib/Drupal/Component/Utility/NestedArray.php).