How do I fix "Failed to unmount /oldroot..." errors when shutting down?

How do I fix "Failed to unmount /oldroot..." errors when shutting down?

I'm on Ubuntu 20.04 latest updates. My boot partition is formatted "W95 FAT32 (Bootable)" in case this has anything to do with the problem.

Failed to unmount /oldroot: Device or resource busy
Failed to unmount /oldroot/dev/pts: Device or resource busy
Failed to unmount /oldroot/dev: Device or resource busy
Failed to finalize file systems, ignoring

Despite these errors, my computer seems to shut off and reboot fine every time. But I would like to clean up whatever is causing these errors.

I've already done sudo apt update, sudo apt upgrade, and sudo apt --purge autoremove, but these errors persist.

Thank you!

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