For what it's worth I just updated AD2 on a Mac running High Sierra.
The update ran OK in terms connecting to the servers etc. but then told me I'd no authorised computers. I thought I had two... Checked my account and I had no listed authorised computers, so I authorised the Mac which went OK. Their site also refuses to let me contact them via their email support form because "that email address does not work, use another". It's the email address I've used as my main one for 20+ years and it definitely works. So I tried entering a brand-new throwaway Gmail address, to be told "that email address does not work use another to contact us".
Looks like something at XLN is badly broken somewhere.
Anyway, might this be related to the authorisation problem?
https://www.xlnaudio.com/...ument-is-in-trial-mode