Yes, it does look like to is an error in the code or an error in the file permissions for the code. My way also works.
I don't know what the URL is for a session restore?
https://chipmixer.com/session/restore/your_session_token_hereI'm getting the same error when I try to manually restore the session.
The workaround is to use the restore link as explained above (which is working fine).