Support suggests to post this here in Ideas:

When editing entries with other layouts than the Default layout and using an input model with full form:
If you open a (descriptive) field and don’t add content (don’t select a picklist item or don’t write any text or delete the text contained in the field, for whatever reason) when leaving the field it disappears instead of remaining there empty.

When actually or in a second moment you want to add data in this field, you have to:
a) choose it again from the list of fields available for this level (and to move it to the right position among the fields of the input model if the position is important, as it is in our case - not intending here the order in which the fields are displayed, this we know can be achieved by the layout, and custom export definitions, but the order in which the fields are actually saved and exported e.g. with default export definition);
or b) to save the entry and open it again to get the field back (in the same position as it was).

If using an input model with full form, also empty fields (which are part of the selected input model) should remain visible in the open entry one is editing; could this be implemented? The "workaround" with saving entry and then reopen is a loss of time. The one adding the field again from the list and moving it to the position it is needed even more so if you have a long list of descriptive fields.

Kind regards,
Klara