It is likely that you now have two passwords manager active at once, as Android allows such a thing.
To solve this, go in Settings → Accounts and at the top of the page you have two sections:
- Preferred service
- Additional services
If you click on the first you will understand what they mean by service, it is actually the passwords manager. Select your previous password manager as the first preferred service and make sure all other passwords manager are deactivvated in the second section to avoid the double prompt you suffer from.