"producer/broker maximum request accumulated, waiting for space" indication of need to increase channel_buffer_size?

I have many "producer/broker/[[1521]] maximum request accumulated, waiting for space" in my filebeat logs, does this mean i need to increase channel_buffer_size? the default value seems very small?
"Per Kafka broker number of messages buffered in output pipeline. The default is 256.", btw, this is the buffer used in the Kafka client library, right? thanks!

btw, there are a bunch of #%!d(MISSING) in my logs, it seems like that msg.Topic, msg.Partition is missing from the code snippet below? i am wondering are those "MISSING"s normal?

2019-07-29T23:55:04Z INFO producer/broker/[[32144 %!d(string=graph-log-exp) 17]] state change to [open] on %!s(MISSING)/%!d(MISSING)

595 Logger.Printf("producer/broker/%d state change to [open] on %s/%d\n",
596 bp.broker.ID(), msg.Topic, msg.Partition)