I have an issue where Piper completely disappears from Sanctuary. The first time I dismissed her from Sanctuary, grabbed Deacon, did a quest, and when I came back she was gone. Searched everywhere, doesn't respond to the bell.

-I've tried dismissing her by both the "Dismiss" option and by choosing another companion. I followed her around and she did what everyone else in the Settlement was doing.

-I've tried dismissing her from outside Sanctuary. It worked at first when I traveled to the Glowing Sea and back. But then I went to Diamond City and when I came back she was gone again.

-She doesn't seem to show up at her old haunt in Diamond City.

I've done some experimenting with Nick and he doesn't seem to have this problem (even after traveling with him and sending him back he comes to the bell). I also can't seem to assign Piper to a bed or for harvesting/guard duties in Sanctuary, despite there being plenty available. Anyone got any ideas about whether this is a bug or some weird AI scripting and how I can work around it?

There seems to be a bug with companions in the game, and a pretty serious one. I'm hoping they fix it.

Maybe try the disappeared Dogmeat solution? Check the all doghouses in Sanctuary.