Help Cannot write to SDcard some moments AFTER starting up

[Yulius]

My SDcard suddenly stopped being modifiable (write [create files, folders etc], delete, rename, copy/paste etc) some moments after startup. Here are some facts:

0) Immediately after startup, I am able to 'modify' the SDCARD. But some moments later (about a minute, after the blue light filter is triggered and the screen turns a little yellowish), I am no longer able to modify the SDcard. Of course, disabling the blue light filter did nothing to fix it.
1) Have tried SAFE MODE. this problem persists even in safe mode
2) It is not an installed apps problem, because I found that the last date I was able to write to the Sdcard using FLUD was 2 March 2019, And I uninstalled every app after that. Used an app called "installed apps" to know the date installed.
3) What was interesting during the SAFE MODE testing was, right after startup, I can create a "new folder", delete it, then create another "new folder", then I CAN'T delete it, after that I was able to create "new folder 1", but when I selected both "new folder" and "new folder 1", and tried to delete them, only "new folder 1" can be deleted, "new folder" stays undeleted
4) What was interesting under my NORMAL MODE testing was, I was able to create a "new folder". But when the SDcard problem gets triggered after a few minutes, the "new folder" got deleted! This didn't happen during the SAFE MODE testing
5) Every app that have the ability to write to the SDcard, including My files (comes from the factory), flud, es file explorer, x-plor, winrar etc, cannot write to SDcard when the offending "setting" is triggered.
6) The Tab s3 is not rooted. Was never rooted, but this problem is new this month only. I've had the tab for 2 years.
7) Some people suggested that I need to "enable" a "documents" app in settings, or "sd card" app in settings, I never found those apps, even after "view all apps" and "show system apps" in settings
8) The closest I got to the apps suggested in 7) is an "external storage" app with "disable" greyed out, which makes me conclude that it has already been enabled and cannot be disabled
9) Kaspersky anti virus found nothing...

Any ideas? Please help guys. I am thinking I probably need something along the lines of a settings trigger log app of some sort to track down the triggering 'setting' that causes this. Or perhaps, a settings log app, that shows when this setting is triggered near the beginning of march, like the case for installed apps.
Any ideas?

 

[bcrichster]

Could be a bad or corrupted sdcard.. Possibly wearing out. I'd swap the sdcard with a new one and see if that helps anything

 

[Yulius]

I actually narrowed it down to the sdcard. Because modifying the card in anyway using other devices such as my windows laptop will also revert it to its previous state upon extracting and reinserting it. It is almost like there is a write protection enabled. But there is no physical slider to enable/disable write protection (micro sdcard).

I can't remove the write protection using gpedit.msc, regedit or diskpart (diskpart shows "read only: no". Which should mean that it is not write protected.).

However, there are no errors when checked using chkdsk.

I have a feeling that this is due to the app recyclemaster I installed around that time but even after I uninstalled it a few days later, it leaves residual settings on the sdcard causing it to be write protected in an unusual way.

Any ideas?