There is a form sections issue where broken relationships between the sys_ui_section and sys_ui_form_section records cause forms to not load. The user deleted a form section, but it still appears on the form.

Symptoms:

Form is not loading or is loading partially. Usually it loads up to a certain related list or related list tab. Records from [sys_ui_form_section] disappear, causing views to break.

Steps to reproduce are not clearly known. In some cases, the issue is observed just after an instance upgrade. The form section appears as a blank entry on the form table.
On the form, when right-clicking Personalize Form Layout, the form section list should show an invalid form section named "label".

The issue is due to a form section deleted from sys_ui_section, but its reference in sys_ui_form_section still exists. The fix is to navigate to the sys_ui_form_section record and delete the entry.

Restore the missing links within the form sections for the specific table where the issue is occurring:

1. Navigate to Forms.
2. Filter for the wanted Table and View that are showing the form sections visibility issue.
3. Click the Table name to open the form sections definitions.
4. Click the Position number to drill down on the individual Form Section detail.
5. Point to the reference icon on the Sys UI section field.
6. If it states None Available, delete that one or restore it to the wanted section, if known.
   For example, from a sibling instance, this can be done by clicking on the magnifying lens and picking the wanted form section from the related list.
   
   Right-clicking and selecting Show XML also helps determine if the referenced form section is valid, showing an existing sys_id. For example:
   
   <sys_ui_form display_value="incident">991f87290a0006414b6521d3fa9b4176</sys_ui_form><sys_ui_section display_value="Notes">991f88d20a00064127420bc37824d385</sys_ui_section>
   
   If the referenced form section sys_id is unknown or missing, find the parent form section sys_id and compare the same record within a sibling instance, when available.
   
   
7. Flush the instance cache.
8. Review or delete the original Update Set that might still contain the invalid form sections linking.
   
   

The following ServiceNow Community discussion provides further information on the data structure behind the form sections:

Discussion: Where are form layouts saved?