scope :sent, any_in(state: [:sent]).desc(:sent_at)
Order.sent.max(:number)

This query raises Moped error:

v3.0.23 - failed with error 15876: "could not create cursor
v3.1.2 - failed with error "no such cmd: aggregate"

This one works:

Order.any_in(state: [:sent]).max(:number) # => 88.0