Buffer utilization is 100% for all nodes having backlog

Graylog Central (peer support)
13

still no luck @jan

But after restart node, I found something in the log.

2018-10-02T20:36:21.580Z WARN  [NettyTransport] receiveBufferSize (SO_RCVBUF) for input BeatsInput{title=Beats - DmsBatchJobs ( Extra Syncer ), type=org.graylog.plugins.beats.BeatsInput, nodeId=hj3c02f5-9878-45b0-a788-8bfe9c9223d2} should be 2097152 but is 212992.
2018-10-02T20:36:21.580Z WARN  [NettyTransport] receiveBufferSize (SO_RCVBUF) for input BeatsInput{title=Beats (Tc's & docker01-04 ), type=org.graylog.plugins.beats.BeatsInput, nodeId=null} should be 2097152 but is 212992.
2018-10-02T20:36:21.580Z WARN  [NettyTransport] receiveBufferSize (SO_RCVBUF) for input GELFTCPInput{title=Gelf Tcp (Dms01, Dms02), type=org.graylog2.inputs.gelf.tcp.GELFTCPInput, nodeId=hj3c02f5-9878-45b0-a788-8bfe9c9223d2} should be 1048576 but is 212992.

What does the number means…?