it appears a nested flex can’t have multiple layouts currently: they don’t get saved. When reopening the field group, an empty layout was added to the parent flex.
After removing that the nested flex content on a page couldn’t be overwritten anymore: It was present as previosly entered but any attempt to change the data was in vain.
I can get more precise:
it does save!
I changed the “field name” of the flexible content field inside the flexible content field.
This lead to the old content disappearing and new inner flex fields all being numerated “0. ” and not saving.
Renaming the inner flex fields field name to its former name made the content appear again.
