If you have to leave a document and return to it during prefill, there is apparently no way to actually return to prefill. I had to look something up and when I came back, it was loading Adobe. Forever. I went back to the sign in menu, and now I cannot access the document. This new interface is really problematic, not intuitive, and not at all a welcome change.
Admingunderwa (Admin, Adobe) commented
Thank you for the feedback. We have made functionality, performance and session improvements which should now resolve the issue. If in case you face the issue again please feel free to reply back.