Maybe is too late but I would use asp-route-Id, like:

<form id="submitfinal" method="post" asp-route-Id="@item.Id" asp-action="Upload" asp-controller="report" enctype="multipart/form-data">

Regards

Maybe it's too late, but I would use asp-route-Id like:

<form id="submitfinal" method="post" asp-route-Id="@item.Id" asp-action="Upload" asp-controller="report" enctype="multipart/form-data">