Delete or Edit buttons may be missing from either the Account or Contact objects: Nonprofit Success Pack (NPSP)

For example: Let's consider the Contact Delete button missing. To fix this you will need to remove the override and then add it back to see the missing button. 

1. Log in to your Salesforce instance.
2. Click on the Setup icon on the top right.
3. Click on Object Manager.
4. Search for and click on the object you're having the issue with (in our case it's the Contact Object).
5. Click on Buttons, Links, and Actions.
6. Scroll down and look at the affected button (Delete).
7. You'll notice that the button is overridden with the CON_DeleteContactOverride Visualforce Page.
8. Edit and remove the override and Save.
9. Now you'll be able to access the Edit button.
10. Once done, edit and add the override the button with the CON_DeleteContactOverride Visualforce Page and click Save.

If you have similar issues with other missing buttons, go to the object you have issues with and fix the issue by removing and re-adding the override as we did for the Contact Object.