It may be fixed. Had to reenable IPN (Instant Payment Notification) on PayPal and provide it with the forums callback URL. I'll know when the next renew kicks in, which should be tomorrow. I shall track it, and see what happens then, and then probably go in and update everyone manually that fell through the paypal-hole.
I was able - at least according to PayPal - to resend the payment confirmation for the following users:
As of right now, it seems to have propagated at least for Kiki, with a delay of several minutes. I am watching the progress and I will have to go in manually for any payment older than 28 days - thanks paypal.
I have manually updated everyone since March 2022, where it apparently last worked properly. I am still waiting for it to maybe work for the aforementioned people, like Kiki, since PayPal claims it should. But Kiki was also the only one-time-payment, who knows if that had an effect. If it didn't propagate by tomorrow, I'll manually set everyone else to Donor.