judging by the document You've provided, the problem is that aircrack-ng uses '-z' by default, which is only valid for proper ARP messages and responses. AFAIUI, to use statistical methods (on IVs that we gathered using our spurious data), we should apply '-K', which result in fallback to FMS/KoreK/Bruteforce method. It require *much* more IVs - at least ~500k for 64 bit key, and ~2,5M-5M for 128 bit key, but it have chance to work actually.

It may seems harsh, but for APs without clients connected, it's still much faster (most of the times) than waiting for someone to connect.

/Estel