If you saved the project at any time, make a backup copy of the AUP file and the _data folder.
If the project has never been saved, look in /var/temp/audacity-username, where ‘username’ is your log-in name, and check that it is not empty.
If it’s not empty, make a backup copy of the entire /var/temp/audacity-username folder.
If the project has never been saved and /var/temp/audacity-username is empty, that’s the end of the story.
If you are able to locate the data, then after making a backup copy of the data and the Autosave file:
Crash exit out of Audacity so that Audacity does not delete any data (from the command line: killall audacity)
Delete all of the “\00\00\00” corruption from the autosave file, and one of the tags. There should be one opening tag for the project and one closing tag to match it. The closing tag for the project is
Then restart Audacity and see if it can recover the project from the modified autosave file.