Hi again Mark,
From your description, this is how a poor quality SD memory card fail after some weeks or months. Good quality SD cards fail in the same way but last for 5-10 years.
Did you get a fast and reputable brand SD memory card, from a reputable seller?
Also, it is not advisable to move the SD card back and forth between a PC and a phone, or to use the same SD card in multiple phones. It should stay in the phone to avoid issues.
If this is a possible explanation then backup your stuff from the SD, format it in the phone and start over...
" it is not advisable to move the SD card back and forth between a PC and a phone"
Why not? I do this ever so often, at least once in 2 weeks, but some times twice in a weekend), I even have cut out an opening into the plastic protective sleeve for the "sliding dock" so that I do not need to remove the phone from the sleeve every time I swap the SDcard.
I have rather large mp3 and mp4 collections (over 70 GB together) that are updated frequently (either new or changed files or changed tags). The only practical way to sync such a very large collection of files is to take the SDcard out and connect it to the PC via an USB3 adapter and then to use a good/ sync application (such as the free FastCopy), this way the syncing usually takes only minutes to say 10 minutes max.
The USB tethered connection between the PC and the phone is not horribly fast, bot the main issue is that there seemingly does not exist any software that can sync the master set from the PC to the SDcard that is in the phone. This is so because via the USB connection the phone can not be mapped as a disk drive in a PC (nor in a Linux) computer.
A cloud service is expensive for large storage space, it is slow to sync and particularly on
travel there is a nasty choice: Not to use the media libraries at all or to pay severely huge transfer fees.
The only reason against swapping the SDcard, that I can see, is that the "sliding dock" feels to be very flimsy so I always fear that I would break it.
Formatting the SDcard in the phone is generally "better" since in some case the phone will not accept a card that is formatted by a computer and therefore in such case the SDcard will be formatted again by the phone. But in the case the SDcard that is formatted in a computer is accepted by the phone then it does not matter, or in fact formatting in a computer has the benefit that the user can choose the size of the Allocation Unit. (Formatting the SDcard as secure storage space always has to be done in the phone, naturally).
What you have to do is to first run plain error checking on the HDD where your original file set is stored. Then if the plain error checking shows that there indeed are errors (this is very likely based on what you have told here) then I would take file backup copies, with verify -option active, of everything important from that HDD to another storage device that is physically another disk/device and not just another partition of that HDD and is know to be in pristine condition, and finally only after all the above I'd do error checking with fix errors -option selected.
@TimoA, thanks for the reply man, but i dont think my files has errors because ive been using it before in my phone until it suddenly misbehave, i think the cause here is connecting my phone to my pc everytime and dont have a proper way to eject it like the usual external storage does, but whats the best and safest way to transfer files then? is it better to eject the sdcard then copy your files? or connect directly the phone to pc? how about my need to connect it as usb internet connection/usb tether?, when using it as a usb tether, my pc would treat it always as a portable storage, and without a proper way to safely remove it, it would just repeat the trouble over and over again.
and as i said before, i came to experimenting in developers option, usb configuration selecting "charging mode" instead of "MTP"/Media transfer protocol, to avoid my phone being read as portable storage automatically, and not having an option to safely remove it. but it would revert itself to "MTP" for sometime.
My post yesterday didn't make it (yet?) so another try without hyperlinks:
File transfer via USB and Media Transfer Protocol is safe to use.
MTP does not require eject, it can't cause file corruption.
(Files can be incomplete if the USB cord is unplugged before it has finished copying but that's another story).
If the SD memory card has been in the phone all the time, and a file has become corrupted over time, then the most plausible explanation is the SD card has become defective.
If in doubt about the health of the phone itself, then I suggest you get it inspected by a qualified technician or a skilled friend.
A skilled friend can also determine if you purchased a genuine, reputable SD memory card that is fast enough for the phone, or whether you got a poor quality, counterfeit, or fake capacity SD card.
@ Hans, my sdcard break once again, by the way, this is the sdcard i brought 3 months ago, "SanDisk Ultra 64GB microSDXC UHS-I Card with Adapter".
Genuine reputable brand SD memory cards come with a limited (money back) warranty, via the point of sale or directly from the manufacturer.
Please refer to the sandisk.com support and their user forum.
The SD memory cards you got so far are probably fake since they malfunction or break after a short time.
SanDisk Extreme with its faster writing speed (and 50% more expensive) is better suited for a Nokia 6, but the Ultra should also work for several years, normally.
It's about the performance of burst-shoot photos, video recording and the general smoothness of the phone and apps.
I hope you get it sorted out.
@Hans, theres one thing i did before it broke down, i use it to video, and when im about to watch the captured video, the sdcard cant be read. for now i dont plan to buy another sdcard, i guess ill just settle with the internal memory capacity. its just sad that i cant use this phone to its full capabilities as its promised. ill just check here for once in a while, if theres someone like me having trouble and did find a concrete solution. Thanks for the help Hans,