It appears that Time Machine couldn't complete the backup to your Easystore drive because of certain files. If you can find these files, you can resolve the issue.
Open Terminal and execute the following command to see the log entries for Time Machine in the last 4 hours.
log show --predicate 'subsystem == "com.apple.TimeMachine"' --info --last 4h | grep Error
Look for the possible files Time Machine was having issues copying, then either delete them or exclude them from the Time Machine backup.
If the issue persists, try removing the backup disk and reconnecting it. For more solutions, continue reading this guide: Time Machine Couldn't Complete the Backup on Mac [Fixed]
