Folder not accessible corrupted or unreadable, driving me nuts!  

This is why I advised the OP to search out more info on the KB issue, from MS and his PC manufacturer's site (Dell is quite good at listing advisories when Windows issues surface), and directed the OP to other 3rd party sites which track Windows update issues.
The checking of cables/ ports is still advisable as is your point about removable media and sleep, only the OP knows all the details about how he uses his PC.
Hopefully with some research and basic trouble shooting/ testing he can pin down the issue.
If you are still following this thread OP, I suggest you try turning off Write caching for all drives while troubleshooting, just one less "fly in the ointment" so to speak.

[Pejole - I agree with you completely. I had not noticed your latest post when I wrote mine - I had a glitch and lost my first draft post so was not paying attention to anything else as I rewrote it. Denis]

No problem.
The more input on this thread, the more options to explore for the OP.

@ Try3
You're right, I read the article more carefully and indeed it's a different case.

Well, I talked to Dell which, for now, suggested to turn off the disk write caching for the SATA hard drive.
I'll test this for a few days to see how it goes.

The disk write caching also reminded me that my UPS unit could be another element to take into account here.
So, for the time being, I'm also disconnecting the PC from the UPS which, from time to time actually beeped apparently for no reason. Maybe was just a mere voltage drop but at this point, I have to consider any possible element.

You could use the Sysinternals utilities to keep an eye on what is happening, they are small free utils that work fine with Win10, particular to your case are some disk monitoring/ exploration utils and one called Process Monitor, this shows a wealth of info about what is happening behind the scenes so to speak, use filters to keep an eye on disk writes and opening processes, you can also log the information and sort by relevance.

Sysinternals Suite - Microsoft Docs

Without a specific plan in place I do not see how they will benefit you.

Denis

I think that Dell advice is inappropriate. You'd have to have a very slow system / drives for you to benefit from turning off indexing but I don't think your system is slow because Dell is talking to you so your system must be fairly new.

I still think you were right on the mark when you were concerned about your cables earlier on. The onset of identical symptoms a few months after replacing the drive followed by slow drive responses seems to me to point to intermittent connections leading to accelerated aging.

Have you tried searching the Dell user forums for your symptoms & your model? There might be similar reports by other users.
Support Forums - Dell Community

Denis

Thank you, Denis

I did search on Dell forum a while back but I couldn't find much.

I was inclined to consider the indexing idea relevant for the only reason that the issues actually manifested after I started filling the hard drive with lots of files. Until then, it worked fine. And it happened within the same circumstances for the previous hard drives as well.

At this point, I'm also considering just moving the hard drive to an external bay and buy an SSD instead.