Freepbx failover issue

Hi Techs, I need your help for this specific issue. I have one active server and one standby or backup server. If active has some network issue then phone registers to standby server. My all extensions are remote. Sometime I face a strange issue, due to an unknown reason, some phones are registers to active and some registers to standy. In this case phones registers to active cannot find the phones which are registers to standby. Is there a way so that phones which are register to active can find the extensions which are register at backup server ?