How to fix the photos missing from iCloud?

Hello. Why did my photos disappear from iCloud? I had an old backup copy, I didn’t create a copy for a long time because I didn’t have such an opportunity, but recently I bought additional space in iCloud, why did my old photos disappear and relatively new photos were saved instead? I don’t know what to do, there were photos of my children, maybe you know what the reason is and you can help me?

[Re-Titled by Moderator]