Hi @clavaque! Since now you have full access to my database, I’d like to let you know this problem happened once again today, user subscribed, s2Member cancelled the subscription a minute later.
I do NOT have any cancellation button as I prefer to ask my subscribers to email me directly instead, so I can double check their subscriptions are actually cancelled, therefore preventing unwanted charges, but this problem is the opposite, the user resubscribes/modifies, s2member likely cancels it thinking it’s a double subscription or something like that. 
I think you have an anti duplicate subscription routine that fails and triggers when it should not. It would be nice to have at least a temporary flag in the settings to disable it, I prefer to cancel duplicity subscriptions manually instead. Would it be possible? Or is it possible to disable that routine with a filter or should I edit the code manually somewhere? I’d rather have the plugin NEVER CANCEL any subscription under any circumstance at payment processor’s level. I prefer to do it always manually. If it happens with PayPal, for example (didn’t see the issue with PayPal) it’s unrecoverable without the user paying again. EOT on wordpress is ok and easy to deal with, of course.