Please check the suggested link in the text description:
which describes generally what are these weak sectors, how they appear, how they could be fixed and repaired - and they could be avoided in general.
Such issues are usually not related to the hard disk drive, but caused by something else: for example connections, cables, power source, overclock, sudden power loss/power failure and so (as described on this page).
Yes, what you wrote is completely "normal" and expected: these pending/weak sectors very frequently cause unreadable files/folders and can lead to boot problems (Windows can't start at all) or "just" such weird error messages/crashes - and may result that the raw read error rate is increasing on some of the drives.
But the problem is generally not the "raw read error rate" itself but the "current pending sector count" which is reported in the text description.
Your repair person would need to address/fix these issues related to cables/connections etc. before (or instead of ...) chkdsk. As described on the link too, chkdsk does not help, does not fix such problems.
Instead, after fixing the cables, connections, you'd need to use Disk menu -> Surface test -> Disk Repair function in Hard Disk Sentinel, ideally then the problems will be fixed and the health may increase too.