Terrain bug

Put the summary of the bug you're having here
When I joined my friends server the ground under me started freaking out.

Describe what you thought should happen here
I think it should be fixed because I cant do anything or build anything.

What actually happened was...: The whole area around my started freaking out as i show in the pictures you get from me.

Describe what happened here* So I joined My friends server and all of a sudden the ground everywhere starts changing rapidly and it went from ocean,beach,forest,underground,duplicating the builds we made to.

Steps to Reproduce:*
1. join the server
2. player gets turned into survival and fall to their death
3. the ground starts to bug out