worlds merged?

hi,

I've been making a banjo Kazooie world for quite a while now. yet when I logged onto it today I found it in a massive crater and the worlds name had changed? I had a world on the old legacy edition which was a super flat 96 blocks tall. my banjo Kazooie worlds name was changed to this one's name. I've had this old world on bedrock for a while now and it hasn't caused any problems yet when I loaded my banjo Kazooie world, apart from the chunks that instantly load, everything was 96 blocks tall. my banjo world originally was the normal height for a super flat.

 

so now everything I've built, which was thankfully in the crater so it didn't get destroyed, is in a massive crater which as far as I can tell goes on forever.