Create a template with 1 snmp item. I created one with a snmp check.

Create an trigger to alert when no data is received for 10 minutes (600 secs)

Apply the template to a host and let it collect data for a good while. (at least 10 minutes)

Verify that at least 10 minutes worth of data has been collected.

Now, remove the template and clear the data "Update and Clear"

Wait a minute or two and RE-ADD the same template back to the host.

You should receive two alerts. One stating that no data has been received in 10 minutes, and the other right after it stating that the condition no longer exists.

It appears that nodata doesn't take into consideration the fact that this is a new application of the template. I also cannot find any additional conditions to apply to the trigger to mitigate this problem.