So it turns out DNSSEC is the problem. Unbeknownst to me, the previous registrar had enabled DNSSEC by default, when I transferred the domain some time ago, the records were not removed when the new registrar updated the nameservers. As they don't have DNSSEC management and my DNS resolver doesn't validate DNSSEC, I didn't notice anything was amiss.
Thank you for your help with this!
