Second content type list is not initialised when using block with nested attributes

Steps:

1. Set up custom block with content type list attribute

   contenttypelist:
      name: ContentType list
      type: contenttypelist
   

2. Edit Landing page.
3. Add custom block.
4. Open block settings.
5. Add second group.
6. Try to expand ContentType list dropdown.

Actual result: It's not possible to expand dropdown.
Expected result: It's possible to expand second dropdown and following.

Remarks: Does not affect v3.3.
Workaround is to submit block settings and enter settings again, then dropdown is initialised.

Update: Affects select also, e.g.:

                            select:
                                name: Select
                                type: select
                                options:
                                    choices:
                                        Foo: 1
                                        Bar: 2
                                        Baz: 3