New SD Card, old content copied but Music and Gallery are empty. LG G5

[Android Central Question]

Hi people! I have an LG G5 (h820) with Android 7.0. So I bought a new, bigger SD card, took the old one (16Gb) out to My PC an moved everything onto the new one (64Gb).

I can see that the files are in the SD from the file browser app and from third party file managers on Android (Total Commander). I can see them from my PC when connected via USB. Even more weird: the music app shows folders, and the number of songs inside them... but when I tap the folder it shows nothing inside. The music library is empty.

I tried restarting the device, both with a full power off, wait, then back on, and also with a restart.
I tried force stopping: Music App, Music Widget, Gallery App and Media Storage App (system).
To all of them, I cleared their cache and their data (force stop first, then clear cache, and then data). After all that I run the gallery and it appeared completely empty (even internal pics missing too xD). Music looked the same.
So I unmounted the SD64, and repeated the force stop, clear and clear. After that, I remounted the SD and run the Gallery, it started populating. I saw the Media storage App data was getting bigger so I waited for it to stop growing. When it finished, the gallery shows only the internal storage images, no pics from SD (except two I just took recently and that are on the same folder with the other hundred pics I took before changing SD).
I'm also able to copy new files onto the SD from internal, rename files and folders on the SD and also view that the files are in the folders and open them: Total Commander has a built in player and can even send the files to some kind of floating Music widget (looks like the Android App btw), files play fine that way but no shuffle and no playlists, which I'm missing.
What is going on?

In the past I had another similar issue in which shredded files (with an app for secure erase) still appeared when connected to PC via USB MTP. I fixed that clearing the Media Storage App Cache and data.
This has nothing to do with the Shredding app as I don't use it since last year, just added this to clarify why I tried clearing the Media Storage data.

 

[Rukbat]

It sounds like a Linux permissions problem. (I assume that you at least restarted the phone once with the new SD card in it.) If the app doesn't have permissions to the folder (or isn't the owner of the folder), it probably can't see anything in the folder. (And if you didn't use a Linux PC, it wouldn't have copied owner and permission data to the new card. [Windows doesn't even know about those things.])

I'd delete the folders on the SD card (whichever ones you have music and pictures in), put the card in the phone, use the apps to create the folders, then copy files over to them from the PC - and see if that fixes it. (Every version of Android gives us new owner and permission problems.)