Replying to myself. That alert didn't trigger b/c when Combination is ANY, an alert only acts based on individual metric behavior, and in this case each individual metric is spiking only every 2 minutes (8 15-sec periods), so, no 2 Periods Over Threshold (POT) occurred in 4 15-sec Observed Periods (OP). If POT is 2, in this case OP must be 8 or greater for the alert to trigger.