To give us some additional clues to go on…
You say you have the same rule in a project and in your My Tasks. To figure out which one is running, click on the word “Asana” here:
to open the rule, then as @Richard_Sather mentions above, copy/paste the URL into a new browser tab and close the rule to reveal the project it lives in. Let us know: is it the rule from the project, or from your My Tasks?
Other questions: once you establish which rule is running, do you have this rule set to run only on tasks or also on subtasks? (This is set via the “Runs on subtasks” option in the rule’s Settings.)
And: is this behavior happening on top-level tasks, or perhaps just on subtasks?