The problem is that generally bad sectors may remain unnoticed for very long time (even years!) until we access (read/write) the appropriate sectors.
Even if we assume that a new drive is perfect, it is not always true.
The Support -> Knowledge base -> Hard disk cases -> Bad sectors ( https://www.hdsentinel.com/hard_disk_case_bad_sectors.php ) describes similar situation, which is generally very common.
Personally this is exactly why I always recommend
1) Test disk drives before real use: general testing of any previously "untested" drive before storing sensitive data. This includes testing new drives and (especially) used/2nd hand storage including hard disks, SSDs, flash drives, SD cards, etc... as suggested at Support -> Frequently Asked Questions -> Hard disk health is low or recently changed or I just installed a new (used) hard disk. How can I perform a deep analysis? ( https://www.hdsentinel.com/faq.php#tests )
This way we can be 100% sure that the drive is really perfect, stable, working correctly - or reveal problems long before failure or "just" corrupted/unreadable data.
2) Always use disk monitoring to constantly check status, report problems, degradations IMMEDIATELY when any, even minor problem happens. Then, when there are only few issues, there is good (much better) chance to stop any pending operations and begin backup procedure to avoid (or at least minimize) data corruption and damaged files. Many users reported that even a relatively good hard disk drive (with 80-90% health) went down to very low health during the backup - and then failed. But with the early notification, they could save most (if not all) data.
In this case it's important to perform file-copy, focusing on most important data first. Not imaging, mirroring, cloning or so, as this is never good idea to be done with a non-perfect drive.
My personal recent experience: a 5 TB very new hard disk showed problems in the last 2% of the disk surface, which could remain undetected until the drive is almost filled. The head stuck on the failing sector (resulting completely non-responding drive) and then, in the following days (due mechanical damages) many sectors around the whole disk surface become unreadable. Of course replaced in warranty - but without disk testing and monitoring 5 TB data could be lost completely - really disaster.
If bad sectors already detected and the status is not perfect, then the best is to
- perform backup
- perform intensive testing (see the above link) to reveal and stabilize issues. If possible (if all data saved), I'd use Disk menu -> Surface test -> Reinitailise Disk Surface test. This would force the disk drive to reallocate as much sectors as possible: repair them and replace from spare area.
This way the amount of bad sectors would not decrease (may increase further) but this way you can be sure that the data area could be used, as the reported bad sectors would be no longer used (instead the spare area will be read/written).
So ideally after this test (which performs general "regeneration" of the hard disk drive - but can be used on SSDs, pendrives, memory cards too) the disk could be better used and further disk tests may show no issues at all.
Then the count of bad sectors (as they are fixed) can be even cleared, so then you'll be notified about possible new issues only.
This is described at Support -> Frequently Asked Questions -> How to repair hard disk drive? How to eliminate displayed hard disk problems?
( https://www.hdsentinel.com/faq_repair_hard_disk_drive.php )
If you are interested further about bad sectors, please check:
https://www.hdsentinel.com/faq.php#health (I have bad sectors and my disk health is 90%. Do I need to worry or ask for replacement drive?)
or click on the "?" next to the text description in Hard Disk Sentinel.