What you need to do is to double-check the path and placement of your `config` into the `Layers.config` file. Look at the below example. 

I need to disable a config file named `training.config`. And this is in the folder `\App_Config\Include\zzz`. 

So I added the location and the path in the `Layers.config` file like this. 

    <layer name="Custom" includeFolder="/App_Config/Include/">
       <loadOrder>
          <add path="Foundation" type="Folder" />
          <add path="Feature" type="Folder" />
          <add path="Project" type="Folder" />
	      <add path="/zzz/training.config" type="File" mode="off" />
       </loadOrder>
   </layer>

So you can see that I used the location under the include folder i.e. `/App_Config/Include/` and then given the path of the file under the `zzz` folder like this `/zzz/training.config`

And this is working for me.

Please check and verify the path and the location where you are adding in the `Layers.config` and try again. 

Also for your config that you have mentioned in your question, I have checked and it's working fine on my local and I have added the entry in the `Layers.config` file like this. 

    <loadOrder>
	  <add path="/Marketing.Assets/Sitecore.Marketing.Definitions.MarketingAssets.Repositories.Solr.Index.Master.config" type="File" mode="off" />
	  <add path="/Marketing.Assets/Sitecore.Marketing.Definitions.MarketingAssets.Repositories.Solr.Index.Web.config" type="File" mode="off" />

Hope this will solve your issue. 

Thanks