Bike chain slips in a strange way I bought a new bike about a month ago. And it made a strange sound from the first ride , I thought the sound was because it was new and will disappear with time but it didn't. The sound is like a sudden collision of the chain with the gears and it lasts for about a second and happens when I am pedaling under pressure ( for example pedaling up hill ) so I filmed the rear part of the chain in slow mo. 

                
            

Some important points: 


the derailleurs are fully adjusted and the shifts work fine 
I tried using WD 40 on the gears but didn't work
the rear derailleur hanger is not bent
the slip happens every about 5 minutes on straight roads and about every 30 seconds on uphills 
At the point of the sound, the pedaling feels very easy for that second ( almost no resistance at all )


Thanks
You can see in the video how the teeth on the cassette rotate quickly at the moment it slips(at :05 seconds), while the spokes of the wheel actually stay slow, then jolt forwards to catch up. This means that the freewheel mechanism in the rear hub is failing to engage. 

It's actually quite dangerous because as it gets worse it could cause you to lose control, fall off etc. in the worst case. 

It shouldn't be like that on any bike, especially a brand new one. So take it back to the shop and have the freewheel, or freehub replaced (whichever type it is).