lately, with my m3 sr+, the walk-up unlock is not reliable. for the first 2 or 3 months, it worked very well, with only the occasional 'who are you, again?'.
the last 2 sw updates (I'm now at the .40 sw rel) do seem to have made the car 'forget' me more.
bluetooth is problematic, and its not really as reliable a set of protocols as consumer may be led to believe, but the last few updates seem to have caused more aggressive sleeping and maybe that's causing the latency. when I take the time to open the app and wait for it to respond, THEN the walk-up unlock always works.