BigQueryWriteClient in DatasetServiceImpl (added at https://github.com/apache/beam/pull/14309) is not closed. This causes the error logs in gRPC orphan channel clean up. See "bigquery_grpc.log" in attachments which is extracted from GCP Dataflow. I don't think this issue affect pipeline runs except the error logs, but could you take a look at that?
A similar issue is reported for CloudBigtableIO at https://github.com/googleapis/java-bigtable-hbase/issues/2658