I get in the console
THREE.BufferGeometryUtils: .mergeGeometries() failed with geometry at index 1. Make sure all geometries have the same number of attributes.
You can only merge if the attributes of the geometries match.
Take a look at the error generation in the file used:
https://unpkg.com/three@0.160.0/examples/jsm/utils/BufferGeometryUtils.js
Update:
Depending on what you need, you can also merge geometries yourself.
An example:
see function link( geoms ) in Pino