indeed that is a tricky one: when you delete that VertexBuffer (Split) you also remove the device for its Mesh (Split) connected upstream (which the vertexbuffersplit magically provides). and what happens is that the Mesh (Split) no longer returns Indices on its second output…see?
and mesh/vertexbuffer operations are done on the gpu so they need a so called device. usually nodes that need a device take that from the renderer that it somewhere connected downstream. but there are some nodes like vertexbuffersplit, pipet, boundingbox,…that don’t have a downstream renderer and those get their device magically via their Device as you can see in the inspektor where -1 means: gimme any device.