Computer Help and Support

Keep in mind that "gallery" is not a location, it is a picture viewing app. It shows you all the pictures located everywhere on your phone.

Step by step to transfer the images using "my files" or "file manager":

Navigate to the SD card.
If needed, create a new folder at: 3-dot menu > new folder
Navigate to the internal storage, to the parent folder of the child folder to copy.
3-dot menu > copy > select the folder to copy > sd card > into the new parent folder > OK

Navigate into the new child folder.
Verify that the pictures did copy.
Restart the phone.

Open the "my files" app.
Navigate to the SD card, verify that the pictures are still there.
Navigate to the internal storage, to the old folder.
Tap the "trash can" icon to start the delete process (or use the 3-dot menu)
select the old folder
tap "delete".
(Verify your work at each step as there is no "undo" of a delete.)

I would restart the phone again.

If the basic gallery app does not work correctly now, there is either something odd going on or you just need a better picture viewing app.
I like "piktures" by Diune:
https://play.google.com/store/apps/details?id=com.diune.pictures

How much free space is left on your internal storage?