Issue shifting from largest cog to second largest Got a Canyon Spectral 3 weeks ago, have done around 2 hours riding on it and have noticed an issue with shifting from the largest cog to second largest. The drivetrain is SRAM NX 1x12.
There are two different scenarios:

When the bike is upside down
The chain will stay on the largest cog no matter how much I shift down, the derailleur does not move when these shifts are done (hence why it stays on the largest cog). If I give the derailleur a gentle push it will then move into gear as the slack is there for it. When it's in a different gear I can go all the way down to the smallest cog fine and back up to the largest. After reaching the largest it repeats the issue.

When riding
When in the largest cog and riding it will shift after around 5 seconds of pedaling on some occasions and almost immediately when cornering like the motion helps it out of the gear. When on the largest cog and clicking shift twice it will skip down into the third largest no problem.


Video of scenario 1. https://www.dropbox.com/s/qs2k2ma9rgvlth4/VID_20181212_184618.mp4?dl=0
I'm already contacting bike shops and canyon have suggested taking it to a bike shop but putting this up to see if anyone has any ideas or has had a similar experience.
I would honestly just take the cable off the and use your thumb to push the derailleur into the biggest gear while turning the peddles. do this over and over again. if it ever sticks then you know its your derailleur. if it does not stick you can move on and look into cable issues.....

hope this helps.