I don’t know what happens but there’s one specific subscription that was fine (modification from free to paid), then s2Member sent Stripe a cancellation request and cancelled the subscription.
I had to override it by manually creating another subscription on Stripe.
A few hours later, around midnight, s2Member sends ANOTHER cancellation request and attacks my manually created subscription, for no apparent reason. 
I know the user did not cancel because I don’t use cancel links or buttons on my site as it’s much more reliable to have the user email me instead, so I know it’s not caused by the user.