• Classic checks for NTP time diff didn't work with active agents.

• Trigger not exist at active templates, but item `

system.localtime` still exist at template. What prevent you to apply another template to check time difference.

• you have own blog post how to solve problem, but it conflict with previous point. https://blog.zabbix.com/time-is-off-active-zabbix-agent/11676/

Solution:

• implement your own trigger or remove useless 
  system.localtime from templates.