Fix #7922

src/Meshes/mesh.ts

@@ -2825,6 +2825,10 @@ export class Mesh extends AbstractMesh implements IGetSetVerticesData {
      * @returns the current mesh
      */
     public synchronizeInstances(): Mesh {
+        if (this._geometry && this._geometry.meshes.length !== 1) {
+            this.makeGeometryUnique();
+        }
+
         for (var instanceIndex = 0; instanceIndex < this.instances.length; instanceIndex++) {
             var instance = this.instances[instanceIndex];
             instance._syncSubMeshes();