Emailer App troubles

Hello,
I'm encountering problems with Notification Emailer App:
I've set up severals instances to warn peaople before the end of subscription (1 month, 10 days, 3 days before the end)
It seems that even if subsriber has renewed his subscription (so that subscription remains active), the email warning that membership is coming to an end is sent.
I'm not sure it is happening for all my subscribers.
Have I done something wrong?
Regards
Simon

Configuration:
Joomla 3.7.3
PayPlans 3.6.0

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