Sorry, but I can confirm that the "programme" completely makes sense
Generally Hard Disk Sentinel designed to detect possible problems/issues related to the storage subsystem - which means other components too (not only strictly the hard disk or SSD).
Exactly as should, the test revealed problems: the current pending sector count increased due to problem in the operating environment.
The text description with the problems displayed this link (maybe you did not check):
https://www.hdsentinel.com/hard_disk_ca ... ectors.php
which clearly describes that while pending sectors can be related to the actual disk drive, in most cases there are something else in the background: cables, connections, overclocking (or even a bad/outdated chipset driver) can cause pending / weak sectors.
And yes, ideally (if the issue is not really related to the disk drive) they can be repaired easily - sometimes they may "automatically" disappear with usage when the drive (re)checks them on a further read/write.
> How can this test be accurate?
This is absolutely wrong question. The test is completely accurate - does exactly what it should: reveal possible issues.
The good question is: what caused the weak sectors and how to avoid (re)appearing in the future?
And this is where the above link could help as it gives details about the background.
If you use Report menu -> Send test report to developer option, it is possible to check the actual situation. This may give some thoughts, eg. depending on the actual chipset and driver - as this may require change. According the experiences such Crucial models are very "sensitive", so they can happily report weak/pending sectors. You may find similar topics in this forum too.
> The drive is rated for 600TBW, and has written 8TB. It has also only been powered on for 44 days.
This is absolutely irrelevant. If there is something in the operating environment (bad cable / connection, not stable power, etc.) then you can expect pending/weak sectors even on a new, unused hard disk drive or SSD.
Alone the fact that the count reduced (so the Health % improved back) suggests that the SSD is working correctly, just sometimes "suffers" from something causing new weak sectors - which could lead to data corruption or "just" reduced performance too. Hard Disk Sentinel increased attention to these - so it does exactly what it should.
You can try to use Disk menu -> Short self test / Extended self test functions. As they run a self test "internally" in the SSD (without transferring data between the SSD and the computer), they generally not affected by cable issues. So these tests will probably report no problems, confirming that the SSD is working correctly - but something during data transfer (like the surface test) can cause troubles.