Another thing you could try that may trigger a reassessment of duplicates is to disable and re-enable contacts from each account, save for the iCloud account.
1. In the contacts app, click on Lists in top left and take note of all the accounts with contact information;
2. In the settings app, go to Contacts > Accounts and click on each of the accounts noted (except for the iCloud account) and toggle off the contacts option in each;
3. Go back to the Contacts app and swipe down while in the Lists page to refresh it (you may need to close the contacts app and reopen to refresh it).
4. Click on “All Contacts” and see if duplicates button is now available under My Card or after last entry (if it is, this will just be a duplicates assessment of your iCloud contact entries);
5. Repeat step 2, this time toggling the contacts option for each noted account to on; and
6. Lastly, repeat steps 3 and 4. If successful, any duplicates assessment should be across all accounts.
Good luck!!