I was resetting a Realm, and at the "new world" option I input a custom seed and loaded the world. As soon as the world loaded it started glitching out, with random things flashing everywhere. It also happened to the other people on the Realm.

Steps to reproduce:
1. Reset a realm's world.
1. Check "new world" and input the seed 7328283878551138757.
1. Make sure the world type is Normal, and structures are on.

Youtube link (low quality): https://www.youtube.com/watch?v=M0LnOked2PM