Cancelled auto-renew membership and scheduled reminders don't play nice
Recently upgraded a site from 4.6.21 to 4.7.27. Payment processor is iATS Payments, if that makes any difference.
When an auto-renew membership is cancelled, the contribution_recur_id field in civicrm_membership for that membership is left as is.
Stated using scheduled reminders after the upgrade, and have one set up to send an email to auto-renew memberships one week in advance of their renewal so they're not surprised when their credit card is charged. Cancelled auto-renew memberships are receiving this reminder.
I honestly don't have time to do any testing or going exploring through code at the moment. For all I know this has been reported previously and is already fixed. But if it hasn't, I'm thinking that contribution_recur_id should be cleared when the recurring contribution is cancelled, or scheduled reminders should make sure the contribution_recur_id is not cancelled.