Ok here is what had happened:
For some reason, the subscription confirmation was no recognized as such, due to an email alias. As soon as it was corrected, the confirmations all matched up with the transactions and all subscriptions were in order.
This was already in order shortly after I changed the alias. Only one member remained of whom the transaction could not be found, but I got the confirmation just now that that was a misunderstanding. Said member had made a donation instead of a subscription :)
So everything got sorted and I enabled the subscriptions button again.