Also, this is a good opportunity to remind everybody about https://status.lemm.ee - you can be sure that I will provide updates on that page as soon as I am aware of & dealing with any issues. I have been posting status updates for the current issue there as well.
Sorry for the inconvenience and I hope you have an otherwise great day!
UPDATE: Hetzner claims they have fixed the issue, but the problems have not been resolved for lemm.ee servers yet, so I am keeping my temporary workaround active for now. Will continue troubleshooting this tomorrow.
UPDATE 2: Hetzner has now fixed their issue, and our network has been restored to its original optimized state.