2025-12-13T01:54:18.150035+00:00 [warning] msg: alarm_is_activated, message: <<“connection congested: #{memory => 47672,message_queue_len => 0,pid => <<"<0.29109602.5>">>,reductions => 139845,send_pend => 82654,peername => <<"111.165.79.26:57048">>,sockname => <<"172.16.196.123:8883">>,buffer => 4096,high_msgq_watermark => 8192,high_watermark => 1048576,recbuf => 131072,sndbuf => 87040,recv_cnt => 158,recv_oct => 5422,send_cnt => 188,send_oct => 956767,username => <<"2699”…>>, name: <<“conn_congestion/Flutter_Ios_269969_00000000-0000-0000-0000-000000000000_fb0879c2-2832-452c-b8e9-afe1c833647b/269969”>>
2025-12-13T01:54:35.955192+00:00 [warning] clientid: Flutter_Android_46199_android:fc712237e5d34c2c89ba61e04acf8733_4203410c-28af-4eb3-b2ec-e7afcd3e5585, msg: socket_error, peername: 112.224.149.132:11021, username: 46199, reason: timeout
2025-12-13T01:54:35.955968+00:00 [warning] msg: alarm_is_deactivated, name: <<“conn_congestion/Flutter_Android_46199_android:fc712237e5d34c2c89ba61e04acf8733_4203410c-28af-4eb3-b2ec-e7afcd3e5585/46199”>>
2025-12-13T01:54:38.604698+00:00 [warning] clientid: Flutter_Ios_244112_00000000-0000-0000-0000-000000000000_e436fd61-d3e2-4581-9438-3c989fb92b57, msg: puback_packetId_not_found, peername: 110.229.66.129:6622, username: 244112, packetId: 24
2025-12-13T01:54:38.636561+00:00 [warning] clientid: Flutter_Ios_244112_00000000-0000-0000-0000-000000000000_e436fd61-d3e2-4581-9438-3c989fb92b57, msg: puback_packetId_not_found, peername: 110.229.66.129:6622, username: 244112, packetId: 24
2025-12-13T01:54:55.414736+00:00 [warning] msg: log_events_throttled_during_last_period, period: 1 minutes, 0 seconds, dropped: #{authentication_failure => 7}
2025-12-13T01:55:54.404001+00:00 [warning] msg: alarm_is_activated, message: <<“connection congested: #{memory => 68480,message_queue_len => 0,pid => <<"<0.27846532.5>">>,reductions => 101052,send_pend => 106835,peername => <<"218.69.156.50:10769">>,sockname => <<"172.16.196.123:8883">>,buffer => 4096,high_msgq_watermark => 8192,high_watermark => 1048576,recbuf => 131072,sndbuf => 330752,recv_cnt => 20,recv_oct => 1861,send_cnt => 139,send_oct => 690235,username => <<"313”…>>, name: <<“conn_congestion/Flutter_Ios_313396_00000000-0000-0000-0000-000000000000_de9d0ed5-a2ff-4ff3-bf5b-f808546e427e/313396”>>
2025-12-13T01:55:54.404919+00:00 [warning] msg: alarm_is_activated, message: <<“connection congested: #{memory => 34888,message_queue_len => 0,pid => <<"<0.27077248.5>">>,reductions => 61664,send_pend => 276958,peername => <<"111.55.146.84:19720">>,sockname => <<"172.16.196.123:8883">>,buffer => 4096,high_msgq_watermark => 8192,high_watermark => 1048576,recbuf => 131072,sndbuf => 46080,recv_cnt => 16,recv_oct => 1748,send_cnt => 70,send_oct => 336639,username => <<"312607”…>>, name: <<“conn_congestion/Flutter_Android_312607_android:9a435b0c71d3499b8501e3f32b58e88d_160491eb-ce03-48c7-8779-3db56d2f5428/312607”>>
2025-12-13T01:55:55.415682+00:00 [warning] msg: log_events_throttled_during_last_period, period: 1 minutes, 0 seconds, dropped: #{authentication_failure => 3}
2025-12-13T01:55:55.605304+00:00 [warning] clientid: Flutter_Ios_269969_00000000-0000-0000-0000-000000000000_fb0879c2-2832-452c-b8e9-afe1c833647b, msg: socket_error, peername: 111.165.79.27:57048, username: 269969, reason: timeout
2025-12-13T01:55:55.606176+00:00 [warning] msg: alarm_is_deactivated, name: <<“conn_congestion/Flutter_Ios_269969_00000000-0000-0000-0000-000000000000_fb0879c2-2832-452c-b8e9-afe1c833647b/269969”>>
发给这个客户端的消息太多了或者网络不好堵了
tcp buffer 里面 pend 了 82654 bytes
buffer 里面都累积了，应该是客户处理不过来，或者是网络不好。然后被断开了。
客户端重连再次上线时（我猜你是用的 clean_start = false）,大量消息会再次发给他。然后断开。如此循环多次，就有了 conn_congestion的告警（短时间内频繁上下线）。
至于那个 timeout，应该就是tcp 发消息超时。
感谢回复我排查下