Also, you might take a look at Settings>Service Settings>OPC Update Rate %. When a group subscribes to values, it subscribes at a percentage of the group rate. I believe the default is 50%, but if yours is set to 100%, you could try setting it lower, like 33%. This means that if the group is set to 1 minute, the opc values will be subscribed at 20 seconds, increasing the chances that the value will come in before the next execution. If you’re having a problem with slow communication, though, this could actually have the opposite effect, as it could add more load.
If you set the group to “only execute once when trigger is active” (on Trigger tab), you should be able to prevent the two executions in a row. However, then you’re potentially opening up another problem: what if the event actually triggers twice in a row? This depends on what you’re tracking. If the events far apart, this isn’t really a problem.