I had the same problem. Was previously sharing the Doorbell fine, but after adding a security camera could not get it to show up on the shared person's account. Ultimately, I uninstalled the app on the other person's phone. Then in my Account I went to Control Center, Shared Users, Manage. Then I removed the shared user. I then sent them another invitation to register with both Ring devices checked. Theoretically, this might've worked if I had just checked the camera (Doorbell was already checked) but I figured it was better to start from scratch. Then I re-installed the app & both devices were showing up. Hope that helps!
I just had this issue on the app, but after about an hour of playing with the app I found the solution (at least for me). At the very top of the app (above the modes) in the middle there should be your Location with a drop down button (I have it saved as Home). If you click that drop down, it'll show you all the locations on your account. If by chance you installed the new item under a new location, you'll have to click on that location to see the camera. I unistalled the device, and reinstalled it using my same location (Home) and now I can see both my cameras without any issues.
Just when we needed the remote access whilst away fora few days, to stickup cam it decided to go offline! The only way to re-instate it was to start over and give it a new name.
THEN although it showed my wife as a shared user her app wanted her to install the camera. Your solution to uninstall and reinstall the app on her tablet worked. Thanks!
What unnecessarily complex software.