It's the new Photos program that replaced the iphoto. Under the View tab, you can check or uncheck the option 'Keep sorted by date.' In iphoto, you had the option to sort by date, title, and a couple other things I don't remember. My photos have titles and I want them arranged alphabetically in my albums, and that option is no longer there.
Also, I can no longer copy a photo, from my desktop or other folder, and paste into Photos, like I could with iphoto. Now it has to be dragged into the album.
They may improve some things on these updates, but they always manage to make other things worse.