>>397830864
Likely dust or dirt on the contacts, very common. Get some electrical contact cleaner spray, there are youtube videos explaining how and where to use it. It's a temporary fix and will need spraying again eventually but it feels like new until then.

>>397830869
They changed the plastic when Quest 1 production ramped up (it's the same controller for both). Oculus recognised that the newer ones were more brittle. This was apparently fixed or possibly it just got swept under the rug by the Quest 2 release. Mine from launch have proven durable against drops and wallstrikes. 
The headset does have some clear usability and durability design flaws in my opinion; For one the tightening knob is small, smooth and offers no grip to sweaty hands. The top headstrap is also only connected to the front of the headset by a thin piece of plastic that will shear off if you keep picking it up by the top strap, as mine eventually did.