Why doesn't Visual Studio 2015 show attachments?

Question

visual studio

Good afternoon!
Created a project in VS 2015. Created folders in the project, added files to the folders. But now, for some reason, through the VS solution explorer I do not see these files. The files are physically present and everything is fine when compiling.
What could be the problem?

UPD: Everything was added via Add Existing Item
UPD1: The problem arose after copying the project to another folder. Returned to the place, everything is ok ...
UPD2: All paths are relative

<ItemGroup>
    <Content Include="Migrate\20160429.txt" />
    <Content Include="Migrate\20160501.txt" />
    <Content Include="Migrate\actual_status.txt" />
    <Content Include="Migrate\address_objects.txt" />
    <Content Include="Migrate\address_object_type.txt" />
    <Content Include="Migrate\center_status.txt" />
    <Content Include="Migrate\current_status.txt" />
    <Content Include="Migrate\estate_status.txt" />
    <Content Include="Migrate\house.txt" />
    <Content Include="Migrate\house_interval.txt" />
    <Content Include="Migrate\house_state_status.txt" />
    <Content Include="Migrate\interval_status.txt" />
    <Content Include="Migrate\landmark.txt" />
    <Content Include="Migrate\normative_document.txt" />
    <Content Include="Migrate\normative_document_type.txt" />
    <Content Include="Migrate\operation_status.txt" />
    <Content Include="Migrate\TextFile1.txt" />
  </ItemGroup>

Answer 1

The problem was solved by deleting all VS settings
In particular files from
user/document/%VSFile%
user/appdata/%VSFile% folders

Answer 2

Visual studio displays the files and folders included in the project. On the folder, click Add Existing Item and include the files you need.

Answer 3

because they have to be added manually. drag and drop files into a folder or via the Add Existing Item menu.