Just to give you a clue. The icons in the comment editor and so are not displayed with me. I assume this is due to external services that have to be downloaded by the user (web fonts?). So this is actually a not relevant individual case.
many thanks for the hints and the link. This information seems to be very useful. The not displayed elements are actually part of the forum, but as I understood it these elements are executed with the help of a script. Probably some scripts have been disabled and therefore these controls are not displayed. Many script blockers are responsible for such problems.