After installing limesurvey I created a test survey with one group and one question multiple choice.
When I try to edit subquestions I get a blanc form.
No button to add extra subquestions just the name of the installation language.

When I hit the button"edit default answers" there is one item SQ001 with a dropbox beneath.

It used to work. I have changed hosting packet(same host firm) so I had to reinstall limesurvey(3.15.5+181115)

If I import a survey with subquestions and I preview the survey I can see the subquestions but again I can't edit the subquestions.

How can I fix this problem?

Do not use version 4.x for production yet, it is fraught with bugs.

Use the latest 3.x LTS version.

found the answer here use php 7.3 instead of php 7.4
( forums.limesurvey.org/forum/installation...t-subquestions-panel )