Thank you.
I had actually already solved the problem using the suggested workaround of opening the STEP file from within Fusion, and then saving the result to the cloud storage. With this method it seems that the STEP-to-Fusion translation happens locally, bypassing the slow cloud conversion altogether.
Even before today's issue I typically see that "uploading" is slow, by which I mean that the actual upload is quick but second half of the progress bar representing the format conversion in the cloud takes many seconds or even minutes. With the approach of opening the file directly within Fusion the process is practically instant. I think this is going to be my approach in future. I do not see a reason to go back to using the upload feature, unless there is something I am missing.