Solution: Disable Steam Cloud Sync
Open your Steam Library and locate Hi-Fi RUSH.
Right-click on Hi-Fi RUSH and select [Properties].
In the General tab, turn off the option “Keep games saves in the Steam Cloud for Hi-Fi RUSH.”
The toggle should appear grey (not blue) when disabled.
Rename your save data folder to create a backup.
Default save location:
C:\Users\<USERNAME>\Saved Games\TangoGameworks\Hi-Fi RUSH
Return to Steam and click [Play] to launch the game.