Missing iCloud Photos

I have an iphone 6s and iphone 11 under the same icloud and apple id. Recently I had my iphone 11 reset and restored my backup however the phtoos from my iphone 6s came up on my phone along with the photos originally on my iphone 11. I deleted the iphone 6s photos off my 11 and they were still there on the 6s. When i would take a photo on the 11 it would also show up on the 6s which was weird but i just left it. After a few days i checked my iphone 6s and all 6000 photos were missing and instead my iphone 11 pictures were there!

Where did my iphone 6s photos go?? I logged into icloud.com and it was only showing the photos from the iphone 11.

Can i get my photos back?? i never turned off icloud photos on any of the devices. Please help!