We apologize for the inconvenience caused, as per the description above, you are not able to upload a PDF file using the Document Cloud service as getting the error message that another instance/operation is in the process, Is that correct?
The record shows that you are subscribed to Acrobat Pro DC subscription with your current Adobe ID, try uploading the file through the URL https://cloud.acrobat.com/ on a different browser like Chrome, or Firefox, or Safari and see if this brings any difference.
You can also upload the file through the Acrobat Pro DC through the icon available on Acrobat toolbar menu.
Is the error message is specific to one PDF file or is it with all the PDF file? Have you tried with other PDF files? Check with other PDF files.
If it is specific to one PDF file, is it possible to share the PDF file with us? To share the file, please use Adobe Send feature, upload the file, share the link to files via private message only, How Do I Send Private Message