It coule be because of lack of availability in Y:

TPE HNL JUL/01 0700 NW ->

[1] TPE HNL 01/0935 01/0935 NW22 J4 C4 Z4 Y0 B0 M0 H0 QC VC LC TC KC [CHG]
[JOURNEY TIME 1080 MIN.]
-------------------- SEPARATOR ------------------------------------------------------------
[2] TPE NRT 01/0935 01/1405 NW22 J4 C4 Z4 Y4 B0 M0 H0 QC VC LC TC KC [757]
[JOURNEY TIME 1035 MIN.]
NRT HNL 01/2035 01/0850 NW10 J4 C4 Z4 Y0 B0 M0 H0 QC VC LC TC KC [744]