Related list for an Object does not appear in Lightning

To display the Related List in Lightning, the Object's Field Level Security must be set to "Read" for all profiles within the Profile Setup.

For instructions, see our "Set Field-Level Security for a Single Field on All Profiles" documentation.

If all necessary permission is given, please consider checking the Profile lightning record page assignment. If the Object is using multiple lightning record page check if the affected profile is assigned to the correct record page which is using the missing Related list component.

To see what record page is displayed for an app, record type, and profile.

From Setup:

1. Go to the Object Manager | Affected Object | Lightning Record Pages
2. Hit Button "View Page Assignments"
3. Under Look Up An Assignment section
4. Check the combination and Hit "Find Page" 

1. Open the affected record
2. Click on the gear icon at the upper right, then click, ‘Edit Page’
3. At the left panel, Drag and Drop the ‘Related Lists’ component to the section you want it to appear on the page, then click Save