zabbix triggers sending message

In zabbix4.2.0 ,i use zabbix web UI Actions create  a triggers to send aler messages . In Operations , i set  step 1-9  and  Step duration 60 ,but it can't work well ... Only work once...When i  set  step 1-0  and  Step duration 60 ,it work well and send mail every minute .Then , i change zabbix's version to 4.0.0 ,it still can't work well , i change zabbix's version(3.4.15) again , only 3.4.15 can work well ! Pls help me solve it !