Owner rashes on "Building Terrain." Other players can still join

Owner rashes on "Building Terrain." Other player can still join.   Owner is using iPad 12.4.   Other player is on MineCraft Windows edition.    There have been no problems for 100+ hours of play.

This happened after a Nether portal use.   Google search found someone with same error.

They said it was fixed after a while, but then your support rep said a server restart was needed.

Thanks