Deleted photos reappear after reboot, new photos dissapear

I try to delete all the pictures I have on my SD card. I just select all of them and click the trash icon. When I finish, I see an empty folder, as expected. I make a new photo. And then I reboot my mobile phone. When I enter the album I see all the photos I deleted, and the photo I created after the deletion is missing.

Why is this happening?

Edit no 1:

Phone: Sony Xperia XA1

Android 8.0.0

I deleted everything from the Album app

Edit no 2:

I unchecked cloud backup, but still have the same problem. I can erase all photos I have, but after restart they still return in seconds.

Where are they stored? Can I erase them manually?

Edit no 3:

Here's what I tried so far. Provided by someone from the talk.sonymobile.com forum:

settings > apps & notifications > all apps > album > storage > clear data > restart the phone > check again.

Did not work.