404 Session not found, when querying Google Cloud Spanner with Python Dataflow.

My Dataflow copies a SQL table with 230M rows into Cloud Spanner. The initial run is successful, but any subsequent run fails with this error. "h1.google.api_core.exceptions.NotFound: 404 Session not found"
and also "504 Deadline Exceeded"

Here is part of the code:

```

SPANNER_QUERY = 'SELECT row_id, update_key FROM DomainsCluster2'

spanner_domains = (
p

| 'ReadFromSpanner' >> ReadFromSpanner(
project_id, database, database, sql=SPANNER_QUERY)

| 'KeyDomainsSpanner' >> beam.Map(_KeyDomainSpanner))

def _KeyDomainSpanner(entity):
row
= {}
for i, column in enumerate(['row_id', 'update_key']):
row[column] = entity[i]
return
row['row_id'], row

```

The Dataflow job is able to read around 10M rows with 2.29.0 but only a few thousand with 2.33.0

Imported from Jira [BEAM-12773](https://issues.apache.org/jira/browse/BEAM-12773). Original Jira may contain additional context.
Reported by: regeter.