The project manually deploys and manages their own proxy contract and upgrades. I strongly recommend that the team use the upgrades plugin from OpenZeppelin instead, because it provides an important feature of validating that the incoming implementations are upgrade safe.
I note that the plugin is part of package.json and was imported into hardhat config file, but am puzzled why it wasnt used (at least in tests).
Strongly consider using the OZ upgrades plugin to manage deployments. More information about its usage can be found in their documentation and UUPS Proxy guide.
An example is provided below:
