On the current list there were about 43000 Subscribers.
And the "Delivery Status" of the members is enabled. Via REST API:
{"address": "http://localhost:8001/3.1/addresses/user@example.com", "bounce_score": 0, "last_warning_sent": "0001-01-01T00:00:00", "total_warnings_sent": 0, "delivery_mode": "regular", "email": "user@example.com", "list_id": "users.lists.example.com", "subscription_mode": "as_address", "role": "member", "user": "http://localhost:8001/3.1/users/c108f28ca58c450ea2c2a91e56b79a3a", "display_name": "", "self_link": "http://localhost:8001/3.1/members/4529b34a6977481b8f9f33efe6e6aa35", "member_id": "4529b34a6977481b8f9f33efe6e6aa35", "http_etag": "\"d36844a7a58a87880efa4f84c90ae3c90df38e29\""}
On another list with the same problem are 63 subscribers.