Subscribers not added to list despite sync

I have "Sync your Shopify email subscribers to Klaviyo" enabled, with "Email List" selected as the destination list. Single opt-in is set (not double).

When I check an affected profile, I see:

• Under Details/Channel consent, it correctly shows subscribed to Email
• Under "Lists and segments," there are zero list memberships — "No results found"
• Under the event history, there's a "Subscribed to Email Marketing" event with a real timestamp

So the consent event is firing correctly, but the profile is never actually being added to the Email List itself, despite the sync being enabled and pointed at that list.

I also just built a new Klaviyo popup sign-up form (also set to add subscribers to the same Email List) — the form's dashboard shows "8 email subscribers" total, but the Email List itself still shows 0 members.

I've re-selected the list in the sync settings and re-saved, with no change. My Email Welcome Series flow is triggered on "when someone is added to Email List," so right now nothing is actually triggering it for these subscribers.

Has anyone run into this gap between "Subscribed to Email Marketing" consent and actual list membership? Is there a setting I'm missing, or is this something that needs a different flow trigger (e.g., triggering off consent status instead of list membership)?