Mirror doing strange things

I haven't used Unity for long time but recently returned to resurrect an old project. I am running Unity 2018.3.3f1 and need to have 3 mirrors in my game where the players can see themselves while they customize their avatar. I started by using the Free Magic Mirror - Lite from the Unity store. The first mirror works great, but the other mirrors show the wrong scene, I see the terrain from a long way off. Like it's rendering from behind the first mirror. I have tried lots of things to stop this, with no luck.

So I found this article http://wiki.unity3d.com/index.php/MirrorReflection4 and followed the instructions to make my own mirror. I haven't tried multiple instances yet as I get this weird effect and am trying to figure it out first.

You can see in the image I uploaded, the mirror on the left is the Magic Mirror, the one on the right is my mirror. Not everything is showing in the mirror, it strips off the front of the face and robe etc, and I also just noticed it is not showing the beams around the door in the background, or some of the parts of the fire pit.

Does anyone have any idea why this would happen and what I can change to fix it? Many thanks.