I've got a new record page with a file upload component conditionally unrendered when the model has unsaved changes. This way it'll render when my user clicks save. Here's the resulting rendered File upload component.
We have ours on a wizard - step one is the record creation. The save button saves the record and then navigates to step 2, where the file upload component is sitting. Not sure why yours wouldn't work, but this wizard method is working for us.
Put the upload component in a separate Skuid page. Put it in a wizard step after record save as a page include. Then the page with the upload component will find an existing record on page load query and maybe trick the upload component.