Custom fields missing on the page related list after deployment via Change Sets

To add them to the related list, follow these steps:

In Lightning Experience mode:

1. Go to Setup | Object Manager
2. Select the object in question
3. Go to Page Layouts and select the desired layout
4. Locate the related list in question, e.g. Campaign History
5. Click on the wrench icon to open its Related List properties
6. From the 'Available Fields' box, select the custom fields you've deployed and click Add to add them on the 'Selected Fields' box.
7. Click OK after it is done.
8. Click Save to save the changes made to the layout.
9. Click on Page Layouts.
10. Click the name of the page layout in question. e.g. Contact Layout

In Salesforce Classic mode:

1. Go to Setup | Customize
2. Locate the name of the page layout in question. e.g. Contact Layout
3. Click on the Edit link.
4. Locate the related list in question, e.g. Campaign History
5. >Click on the wrench icon to open the Related List Properties.
6. From the 'Available Fields' box, select the custom fields you've deployed and click Add to add them to the 'Selected Fields' box.
7. lick OK after it is done.
8. Click Save to save the changes made to the layout
9. Click the down arrow for the object in question. E.g. Contacts
10. Click on Page Layouts.

If you open a record (The above example is for a Contact), you should see on the related list section (Campaign History Related List) the fields you have deployed and manually added.