I've had both of those things happen to me.
After I was ghosted, it really made me question my own self-worth and if I had misled myself to believe that there was a relationship. When that person came back, it was like a prayer had been answered. But as time went on, I saw him for who he really was. No way can this guy meet me at my level. I realized that my attraction to him and the unbearable heartbreak I felt after being ghosted was because I had an unhealthy attachment.
The term is "zombie", not because they come back but because when they do, they're never as good as how you remembered them.
I don't know why but we tend to put those who ghosted us on a pedestal. When they come back, if you give it enough time to really know them, you'll see that they don't quite measure up to you.