kinesis -> lambda -> ES only posting some records

I setup a simple config to test this out:

logstash-forwarder -> logstash -> kinesis -> lambda -> ES

For batches of size 1, this works fine, log lines are pushed to ES in a few seconds.

For batch size > 1, I am seeing inconsistent behavior, with one of some of my records being pushed. It's often about 5 records that make it through but it's not consistent.

In my lambda logs I sometimes see `Error: Error: socket hang up` a number of times, corresponding to the number of missing records, but this too is inconsistent.

I've confirmed that the expected # of the records appear in the kinesis stream and are transmitted to the lambda job.

What am I doing wrong? Is my kinesis stream too small? My lambda timeout too short?