Form layout misconfiguration can lead to sys_ui_form_section and sys_ui_section records disappearing.
The following misconfiguration is seen in several use cases, possibly due to the Form Designer:
View A will have a form defined for Incident that has several sys_ui_form_sections pointing to sys_ui_sections with the view defined as View A.
View B will have a form defined for Incident that has several sys_ui_form sections pointing to the same sys_ui_sections in View A, or just some of them.
The relationship does not cause any issue with the form rendering. The main problem is that the relationship can exist in the instance without the administrator knowing, and when a form layout change is made (for example, adding/removing a field, reordering), the sections disappear and leave the form in an unusable state.
Go to sys_ui_view.do and create two new UI Views: View A and View B.
Create incident forms for both views based on the Default view.
Go to sys_ui_section_list.do and delete the record for Related Records from View B.
Copy the sys_ID of the record for Related Records from View A.
Go to sys_ui_form_section_list.do and use the sys_ID to set the relationship for Related Records in View B.
The two forms should now share sys_ui_section records for Related Records but have their own copy of everything else.
Make a change to the form layout of both views.
One or both updates will cause the form sections to disappear.
Delete the invalid form sections for the affected table and view, and then manually re-create them using the Configure Form Layout feature.
For more information, see KB0534762, "Form Sections configuration - Broken relationships between [sys_ui_section] and [sys_ui_form_section] records cause forms to not load."