arranging my photos and images in Photo... how can I order them manually in the sequence I want?

While in iPhoto it was easy to drag photos to order them how I want them in an album, it seems in Photo I only have three options for arranging photos... by date (newest or oldest) or by name.

But my albums are a medley of random images, and I want them in a specific order. Yesterday the software was letting me drag these and put them in the order I want, but today - as soon as I move an image - it pops right back to where it was... this is so frustrating! I have tried every combo of holding down control key, shift key, etc, while I move an image into order... but nothing is working. The thing is that most of the 70 images I have in this folder are already in order (as it seems it worked until I added some new images to the folder today.) Today it is all going wrong, and if I trying changing the option to "Keep sorting by name, or date etc" it could mess up the order of all 70!

Any ideas would be much appreciated!