I faced the similar issue, it was due to the `dataprovider` configuration at the database level.

Starting from `Sitecore 10`, the dataprovider contains 2 params `headProvider` and `readOnlyDataProviders` and should be of type `CompositeDataProvider`. In order to patch the dataprovider configuration, it should be configured under the `headProvider` param as below.

```
<database id="web" role:require="Standalone or Reporting or ContentManagement or ContentDelivery">
  <dataProviders>
	  <dataProvider type="Sitecore.Data.DataProviders.CompositeDataProvider, Sitecore.Kernel">
		 <param desc="headProvider">
			<dataProvider param1="$(id)">
				<prefetch hint="raw:AddPrefetch">
					<patch:delete />
				</prefetch>
			</dataProvider>
	    </param>
	 </dataProvider>
  </dataProviders>
</database>
```

You can make sure the custom `data provider` added inside your solution, inherits the above structure to avoid duplication of content items.

Hope this helps!!! Let me know in case you face any issues.