As a proof owner if you need to reopen a manually archived proof to where it was last at, you can.
To reopen the proof:
Open the proof’s info pane either by clicking the info icon on the proof tile, or when you’re viewing the proof.
Click the cog icon to manage your proof.
Click reopen proof.
Click yes, reopen to confirm.
The proof will be reopened to continue from where it was last left off.