You have created a monitor set and have checked the "Enabled Counter Matching".
You have assigned the monitor set to a machine.
When you go to the Monitor tab -> Monitor log page, you do not see this monitor set listed
Enable Counter Matching means that Kaseya will only apply the monitor set if the values in the monitor set match exactly what is on the machine that you are trying to monitor.
For example, if the monitor set is checking "Logical Disk", but the machine that you have applied this to is another language, so that Logical Disk is called "Logische Schijf", because these do not match exactly, the monitor set will not apply.
WORKAROUND / RESOLUTION
Disable "Enable Counter Matching" on this monitor set, and re-apply.
TIPS AND TRICKS
If the monitor set is applied to 99% English machines, but you have a couple of non-English devices, you can use the Individualised monitor set option to change just these machines. See this KB article - https://helpdesk.kaseya.com/entries/104700963-How-can-I-change-the-monitoring-of-certain-counters-without-changing-the-whole-monitor-set