Double check Game\Server\src\rooms\schema\RaiderRoomState.ts
I bet there is a require somewhere in there.
Here is a sample of how I import the vector 3
import { Vector3, Color3 } from ‘@babylonjs/core/Maths/math’
All of that said, I found using es6 imports of Babylon libraries to be more trouble than it’s worth. So I went back to including the CDN library in the header of the HTML.
See this thread Babylon.js bundle size for reasonably minimal project?