On some Android devices, you may see duplicate notifications for the same campaign. Something like this:
This happens due to Physical web being turned on for your account. The Google Nearby app picks up notifications for both Nearby as well as Physical Web. You can read more about Physical Web and its uses in the linked article.
If you choose to, you can turn off Physical web to stop duplicate notifications. You can do so from your dashboard by clicking on the toggle switch under Account.
Note: If you turn off Physical Web your notifications will stop reaching devices that do not have their device language set to your notification's default language.
To prevent this from happening you will need to edit your notifications to support other languages under the Eddystone Notifications section on the Beacon detail page by clicking on Add Language.