num_instances Metric is identical to num_inferences Metric

Compare how both metrics are incremented:

https://github.com/tensorflow/tfx-bsl/blob/05edfd1fffd7b0559f6b64658ff79371efeae07b/tfx_bsl/beam/run_inference.py#L269

and

https://github.com/tensorflow/tfx-bsl/blob/05edfd1fffd7b0559f6b64658ff79371efeae07b/tfx_bsl/beam/run_inference.py#L270

This doesn't seem correct.