why I can delete certain pictures from my hidden pictures

Where did the pictures you can't delete come from? If you synced them to your phone using iTunes or Apple Devices or Finder, you can't delete them on the phone directly. You have to use the method you used to sync them originally to unsync them.

Good evening,

Have you checked that there are no problems with photo synchronization on iCloud?

Have you checked whether, when you try to delete the photo, it disappears only on one device or whether it disappears from all devices (iPhone, iPad, Mac, etc.)?