Why is Google Cast interrupting my app and refusing to go away?

[AC Question]

It is "hacking" my app, for lack of a better term, with a pop-up and not allowing me to use the app until I enter a 4 digit code to cast to a nearby device. Only I don't have a Chromecast device and would therefore like the pop-up to go away and never come back again.

 

[rcpa]

My daughter's Galaxy S7 has been doing this for the past couple of weeks. It happens several times a day. She has to reboot her phone to make it go away, but then it comes back several hours later. Tried factory resetting her phone today, but it's still happening. Would love to know how to make it stop.