Can you share a screenshot of what the second subflow (the one that stops) looks like? Perhaps you are missing a Launch new Microsoft Edge action there. Or, you may have used it to create a new browser variable, but the action that fails may actually be using the one from the previous subflow that has already been closed.
So, pay close attention to whether you always launch the browser, as well as whether you use the correct browser instance variables in your actions.
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