@Sebastiaan thanks, I've checked this (also with my other package which doesnt have that issue) and I've got exactly this code in it :

<Content Include="App_Plugins\SvgSpritePicker**\*.*">
            <ExcludeFromSingleFile>true</ExcludeFromSingleFile>
            <CopyToPublishDirectory>Always</CopyToPublishDirectory>
        </Content>
        <None Include="build\**\*.*">
            <Pack>True</Pack>
            <PackagePath>buildTransitive</PackagePath>
        </None>