Writing this from the Crown Lounge, not issue at all to get in. The agent scanned the AtlasGlobal boarding pass without question and typed my FF number into the computer.
Online check-in was working also on the Atlas Global website, despitie of KLM's info on https://www.klm.com/travel/nl_nl/plan_and_book/ticket_information/Flying_with_KLM_partners/index.htm#p14