'why the trigger on change doesn't work correctly?

I have set a trigger on change when a cell is> 0. This cell is the only cell for this sheet and it comes from an importrange formula. The system sends the mail correctly because the value becomes 1 but now it sends me the mail every 15 minutes !!.. Maybe for the script the "importrange" formula is read as a change in the sheet even if nothing changes? how can i do to solve? thanks enter image description here



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