Why these bend lines are visible in 3D model's flat-pattern(OK) but not when creating a flat-pattern in drawing-mode ?
First, compare the settings you have for Flat Pattern Display in the Sheet Metal application and in Drafting - the settings are separate.
Sheet Metal-->Preferences-->Flat Pattern Display
However it looks like only some of the bend lines are missing. Can you upload a part file so we can take a look?
If you re-create the flat pattern view, does that fix the problem? It might be down to when the flat pattern was created (looks like you're on NX9). Is this part created from an earlier version? You have IDEAS views in your model views.
It looks like there's bend line annotation missing in the 3D view as well - perhaps this is related. You mentioned that nothing is hidden, but have you checked to see if all layers are visible in the view(s)?