Regularly, proxies loose their configuration, with no hint in log.

Server log : (just look at the datalen to proxy bt1svluy)

$ grep -v " active checks " /zabbix/log/zabbix_server.log | grep -v supported
23574:20140210:140007.144 Sending configuration data to proxy 'bt1svltk'. Datalen 12416167
23553:20140210:140807.396 Sending configuration data to proxy 'bt1svlfp'. Datalen 40505762
23551:20140210:140925.076 Sending configuration data to proxy 'bt1svluy'. Datalen 24201385
23539:20140210:141015.042 Sending configuration data to proxy 'bt1svltk'. Datalen 12417193
23546:20140210:141832.616 Sending configuration data to proxy 'bt1svlfp'. Datalen 40499784
23584:20140210:141940.942 Sending configuration data to proxy 'bt1svluy'. Datalen 24201892
23561:20140210:142022.827 Sending configuration data to proxy 'bt1svltk'. Datalen 12417697
23494:20140210:142353.887 enabling Zabbix agent checks on host [bt1shl0n]: host became available
23496:20140210:142353.993 Zabbix agent item [system.swap.size[,free]] on host [bt1svlgv] failed: first network error, wait for 15 seconds
23523:20140210:142408.636 Zabbix agent item [system.swap.size[,free]] on host [bt1svlgv] failed: another network error, wait for 15 seconds
23526:20140210:142423.665 Zabbix agent item [system.swap.size[,free]] on host [bt1svlgv] failed: another network error, wait for 15 seconds
23516:20140210:142438.683 Zabbix agent item [system.swap.size[,free]] on host [bt1svlgv] failed: another network error, wait for 15 seconds
23561:20140210:142857.094 Sending configuration data to proxy 'bt1svlfp'. Datalen 40500039
23556:20140210:143007.136 Sending configuration data to proxy 'bt1svluy'. Datalen 8474 <---- HERE !
23551:20140210:143030.797 Sending configuration data to proxy 'bt1svltk'. Datalen 12417948
23487:20140210:143507.767 Zabbix agent item [system.swap.size[,free]] on host [bt1svl46] failed: first network error, wait for 15 seconds

proxy log :

$ grep -v " cannot send list " zabbix_proxy.log
16316:20140210:141941.303 Received configuration data from server. Datalen 24201892
16316:20140210:141944.334 slow query: 2.200788 sec, "select itemid,type,snmp_community,snmp_oid,hostid,key_,delay,status,value_type,trapper_hosts,snmpv3_securityname,snmpv3_securitylevel,snmpv3_authpassphrase,snmpv3_privpassphrase,formula,logtimefmt,delay_flex,params,ipmi_sensor,data_type,authtype,username,password,publickey,privatekey,flags,filter,interfaceid,port from items"
16316:20140210:141951.152 slow query: 3.665835 sec, "select i.itemid,i.hostid,h.proxy_hostid,i.type,i.data_type,i.value_type,i.key_,i.snmp_community,i.snmp_oid,i.port,i.snmpv3_securityname,i.snmpv3_securitylevel,i.snmpv3_authpassphrase,i.snmpv3_privpassphrase,i.ipmi_sensor,i.delay,i.delay_flex,i.trapper_hosts,i.logtimefmt,i.params,i.status,i.authtype,i.username,i.password,i.publickey,i.privatekey,i.flags,i.interfaceid,i.lastclock from items i,hosts h where i.hostid=h.hostid and h.status in (0) and i.status in (0,3)"
16316:20140210:143007.137 Received configuration data from server. Datalen 8474

alternate server log view :

$ grep bt1svluy /zabbix/log/zabbix_server.log
23553:20140210:135924.884 cannot send list of active checks to [172.21.20.114]: host [bt1svluy] not found
23542:20140210:140124.928 cannot send list of active checks to [172.21.20.114]: host [bt1svluy] not found
23541:20140210:140324.968 cannot send list of active checks to [172.21.20.114]: host [bt1svluy] not found
23584:20140210:140532.009 cannot send list of active checks to [172.21.20.114]: host [bt1svluy] not found
23584:20140210:140732.048 cannot send list of active checks to [172.21.20.114]: host [bt1svluy] not found
23551:20140210:140925.076 Sending configuration data to proxy 'bt1svluy'. Datalen 24201385
23568:20140210:140932.091 cannot send list of active checks to [172.21.20.114]: host [bt1svluy] not found
23556:20140210:141138.355 cannot send list of active checks to [172.21.20.114]: host [bt1svluy] not found
23572:20140210:141338.400 cannot send list of active checks to [172.21.20.114]: host [bt1svluy] not found
23562:20140210:141538.450 cannot send list of active checks to [172.21.20.114]: host [bt1svluy] not found
23556:20140210:141746.352 cannot send list of active checks to [172.21.20.114]: host [bt1svluy] not found
23584:20140210:141940.942 Sending configuration data to proxy 'bt1svluy'. Datalen 24201892
23553:20140210:141946.392 cannot send list of active checks to [172.21.20.114]: host [bt1svluy] not found
23548:20140210:142146.457 cannot send list of active checks to [172.21.20.114]: host [bt1svluy] not found
23626:20140210:142401.769 item [bt1svluy:vfs.file.size[/appli/zabbix/zabbix.db]] became not supported: ZBX_NOTSUPPORTED
23556:20140210:143007.136 Sending configuration data to proxy 'bt1svluy'. Datalen 8474
23574:20140210:144918.007 Sending configuration data to proxy 'bt1svluy'. Datalen 21693