Custom subdomain connection fails with portfolio.adobe.com/missing despite correct DNS (24h+ propagated)

I'm trying to connect a custom subdomain (not a root domain) to my Adobe Portfolio site, and the connection keeps failing even though my DNS configuration matches Adobe's instructions exactly.

Setup:

• I want a subdomain (e.g. sub.mydomain.com) to point to my Adobe Portfolio site, while the root domain stays hosted elsewhere (WordPress).
• In Settings > Domain Name, I entered the subdomain and added the 4 required A records exactly as provided (2 for the subdomain host, 2 for the www.subdomain host), pointing to the two IP addresses Adobe gave me.
• I removed any conflicting old records on those specific hosts, and there's no CAA record blocking anything.

Result:

• DNS resolution is confirmed correct and fully propagated (verified independently via direct DNS lookup, not just waiting) — it resolves to the exact same IP addresses as my default myportfolio.com URL.
• Despite this, visiting the subdomain redirects to portfolio.adobe.com/missing, and Settings > Domain Name still shows a validation error specifically on the www subdomain.
• This has persisted for more than 48 hours, well beyond the usual propagation window.
• My site itself is published and live at the default myportfolio.com address, so that's not the issue either.

Has anyone else run into this specific "DNS is correct but validation still fails" situation with a subdomain (as opposed to a root domain)? I've already opened a support ticket but haven't had a resolution yet, so I'm hoping someone here has hit the same wall.