Photos disappeared from shared library

I have a shared library with my wife and kids since some time. Yesterday most of mine and my kids' photos disappeared from the shared library and our personal libraries.

Naturally we panicked, but later found that the photos "moved" to my wife's personal library. She hasn't moved them voluntarily - nor should have the option, because the photos were not made by her.

Anyone had the same issue? Any advice how to proceed - is it safe to move the photos back to the shared library?