Disappeared photos from iCloud

Hi guys!

Yesterday I noticed that on my iPhone 6s the gallery of photos only showed around 100 photos our of 9000 that I used to have. The photo gallery is connected to my iCloud, hence at first I though it was a synchronization issue, but when I checked my iCloud, i noticed that they are disappeared from there as well.

I checked in the recently deleted files but nothing. I cannot explain myself how this happened. I have tried to restore my phone with am iCloud back up from last week, but similar story. At first, it recognizes 9000 pictures, but I cannot open most of them. With time, it reduced the number of pictures in my gallery until it gets back to around 100. It looks like it sees the pictures and the albums are there, but it cannot recover the files and then they disappear.

Does anyone of you experienced something similar? Do you know how to recover missing files on iCloud? I have been reading online but so far no solution seems to work. Thank you in advance.

Best,

Matteo