We have observed intermittent occurrences of the error "Session not found" when attempting to send requests to Spanner. The Keep Alive interval is set to 60 seconds, which should ensure session persistence.

The application interacting with Spanner is deployed across three pods. The Client Spanner configuration is as follows:

SessionPoolMinSessionsOption: 100
SessionPoolMaxSessionsPerChannelOption: 400
SessionPoolKeepAliveIntervalOption: 60 (seconds)
GrpcNumChannelsOption: 4