Relevant CTS tests:

webgpu:api,validation,encoding,cmds,render,draw:vertex_buffer_OOB:*
webgpu:api,validation,encoding,cmds,render,draw:buffer_binding_overlap:*
webgpu:api,validation,render_pipeline:vertex_state:*

wgpu requires (most notably here, but it's also implied elsewhere by non-Option arrays for vertex buffer slots), that vertex buffers be placed contiguously in slots 0..N-1, but this requirement is not specified by WebGPU. The CTS tests above use only vertex buffer slots 1 and 7. They fail with errors like:

In a draw command, kind: DrawIndirect: Currently set RenderPipeline with '' label requires vertex buffer 0 to be set

and:

In a draw command, kind: Draw: Instance 200 extends beyond limit 0 imposed by the buffer in slot 0. Did you bind the correct 'Instance' step-rate vertex buffer?

I am not sure if the second symptom is entirely due to this issue, or is partly due to some other problem.