Is it possible for you to paste the trigger condition you have and what your expected outcome is? There are definitely ways to trigger off of multiple nodes but it just depends on what kind of logic exists to build the condition. I'm an engineer with Loop1 and we provide professional/consultative services for SolarWinds. I have a bit of spare time today if you'd like to message me I can work on it with you at no cost. Contact info below.
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As mentioned by @kboldizar we would need a little more information.
It is likely the additional node(s) you are trying to include does not match the same criteria as the successfully triggered node, and you would have to find the common criteria or adjust the alert logic to include it.
Here is some information that might help: