2 questions: [1]Does fastboot need to be off , [2]disappearing backups

[admin]

First, you do not need to turn off Fast Startup before backing up. Regarding the issue of the backup image disappearing, we think you should first ensure that your USB drive has no quality issues. Then try the following to determine the cause:
1. Use shorter filenames to see if the problem persists, though we don't believe this is the cause.
2. Try another USB drive to see if the problem persists.