Steps to reproduce:

Wrong trigger prototype 

: Disk is overloaded

Using min(/Windows by Zabbix agent active/perf_counter_en"\PhysicalDisk({#DEVNAME})% Idle Time",60,15m)>{$VFS.DEV.UTIL.MAX.WARN} 

but 

Physical Disk% Idle Time

The % Idle Time counter is the percent of time that a disk was idle during the sampling interval. An idle time of less than 20 percent indicates that the disk may be overloaded.

So, the right body should be like this:

max(/Windows by Zabbix agent active/perf_counter_en"\PhysicalDisk({#DEVNAME})&#37; Idle Time",60,15m)<{$VFS.DEV.IDLE.MIN.WARN}

Where {$VFS.DEV.IDLE.MIN.WARN} = 20