That is a good question.
In theory, you should be able to manually downgrade. BUT, I don't know if there have been any updates to the database from LS 3 to LS 4 beta, and if so, if they have any impact on downgrading.
Are you a user of comfort update (paid)? If so, you could get in touch with Limesurvey GmbH and see if Louis has some feedback on how to best downgrade. You could create a support ticket (go to "Support" on the top navigation). But it should be quite late in Germany already, so you might have to wait until tomorrow.
As you are live, I guess you need to solve this rather sooner than later.
Another option could be, that your survey design template does not work well with LS 4. As far as I know, there shouldn't be any problems, but who knows.
If you are using a custom template, try to use one of the shipped templates and see what happens.
One other thing to look at: What is the value of "subquestion width" in this specific question?
www.limesurvey.org/manual/Question_type_...subquestion_width.29