The bug reportedly impacted past versions of the macOS Big Sur installer, and appears to date back to the first shipping versions of macOS Big Sur that launched in November 2020. Because past installers failed to check for available disk space, they'd continue to run through the installation process until all available storage was exhausted. That resulted in an install loop, and possible data loss. Macs required at least 35.5GB of free space to upgrade to macOS Big Sur, not including the 13GB installer itself. According to Mr. Macintosh, users have been complaining about the issue since November 2020. Although there were some data recovery methods available to affected users, most had to fully erase and reinstall macOS on their machines.