Pardon my rudeness, I didn't check your post count. I too, welcome you to the forum.
Not sure why you are losing you thumbnails.
I just tried moving a folder. The folder shows up in the left panel in red text. If I click on it, I get my thumbnails. In the upper right corner of each thumbnail is a "?". If you click on that, you get a pop-up window that asks if you want to locate the photo. Follow the navigation to where you have moved the folder. Click on the correct photo. Confirm the move by clicking on SAVE. At this point the folder will move on the left panel & the photos will show in their new location. It should find all the photos in the folder even though you have only indicated the path to 1 of them.
Hope this helps