I'm running, not 3.1.4.
We have to build your case with a minimum of information (across multiple time zones), so having a mistake anywhere can cause a lot of confusion.
I also opened the project.aup file in a text editor and updated the projectname attribute to be identical to that of the .aup file.
Did you get all of them? That's not recommended. You should use the listing at the top of the AUP file (the original, real name) and change the name of the AUP file and the name of the _DATA folder to match.
You are correct. They have to be in the same location or folder. They have to be named the same and it has to be the name you gave them inside Audacity (or you have to get lucky).
Did you keep all the original files in case you had to back up and start the rescue process over?
Audacity hates external, network, and cloud drives. It's not arbitrary. Audacity assumes that whatever drive you assign to it can handle the most important, critical, time-constrained jobs. That's not possible if your cloud drive is in the next time zone. So if you do have actual data damage that's probably where it came from. Audacity doesn't understand network collision detection and resend management. Stay on your internal drive until you're finished.
Was this job an edit? If it was then the possibility of total rescue is zero. Sometimes, under certain circumstances, and with the proper magic spells, you can rescue most of a damaged,
unedited recording. There have been shows posted on the forum which came back. But those are unicorns.
You should decide what you're going to do if the show doesn't come back in a usable form.
Koz