nodejs-spanner: TypeError: Cannot read property 'type' of undefined at SessionPool.getSessionGroup_

I have a cloud function deployed on GCP which is triggered by Cloud Pub/Sub topic. It connects to cloud spanner to insert the pub/sub event data. It is a high volume pub/sub topic and make simultaneous insert requests in different cloud spanner table. However, it keep giving below errors intermittently.

ERROR: TypeError: Cannot read property ‘type’ of undefined at SessionPool.getSessionGroup_ (/user_code/node_modules/@google-cloud/spanner/src/session-pool.js:709:17) at SessionPool.spliceSession_ (/user_code/node_modules/@google-cloud/spanner/src/session-pool.js:865:20) at SessionPool.borrowSession_ (/user_code/node_modules/@google-cloud/spanner/src/session-pool.js:419:8) at SessionPool.getNextAvailableSession_ (/user_code/node_modules/@google-cloud/spanner/src/session-pool.js:648:8) at /user_code/node_modules/@google-cloud/spanner/src/session-pool.js:936:19

Below are the dependencies in package.json

{
        "dependencies": {
                "safe-buffer": "5.1.1",
                "@google-cloud/spanner": "1.3.0",
                "google-gax": "^0.14.5"
        }
}

Thanks for your help.