After a lot of testing I think I've figured out that the problem with this paragraph is that once created, the content can no longer be edited. Every attempt to edit and save gives the error message "Nicht zu übersetzende Felder können nur durch eine Aktualisierung der aktuellen Revision geändert werden.". Edits I've tried include:
editing block text field
adding an additional block
adding an image to a block
editing the paragraph title and kurzbeschreibung seem unaffected. So tbh this is likely a problem with the "Block" pargraph