Creating invoices, changing the dates of payment and marking invoices as paid

The Membership is creating invoices by itself and changing the dates of payment

marking invoices as paid when those are not.

I have this invoice, but I don’t know when the user paid. It is not linked to a gateway and I can’t find the transaction.

I’m also receiving from IPN (PayPal) a lot of: ‘Duplicate: Already processed that transaction’