I chimed in on an identical post, but encountered more issues after the 4.1.0 update, so I created a new post here.
I just updated to v 4.1.0 today and cannot add new fields or copy existing fields and save. With v 4.1.0, the newly created fields did not show in the field list. When on the field details page and after save, the detail page refreshes, clears the Item Name box, but does not return to the field list screen. When manually returning to the field list, the new field is not displayed and of course, cannot be accessed.
Rolling back to 4.0.9 until this is fixed.
After rolling back to v 4.0.9, the fields I created under v 4.1.0 were present and displayed in the field list. However, all previously existing fields are now missing from the event field list and only the newly created fields display. The fields all exist in the database, but now do not display on the admin site and they are no longer present on the front-end registration forms.
We need a quick solution to this as we have a major event scheduled to go live in several weeks.