Nokia Lumia 930 Defects or Firmware Issues

Question

I recently upgraded to a Nokia Lumia 930, I had a 920 for ages and loved it. However, I had to replace my first 930 within two days as there was a hardware issue with one of the back buttons not working (when the phone heated up the back button would start pressing itself and get stuck sometimes).
I've had the new Lumia 930 (the replaced one) for two months now and the following problems have come to my attention:
Double tap to wake goes through phases where it just does not work. I've tried pressing down on the top right corner to see if it rectifies the problem but it does not (not sure how double tap to wake uses the proximity sensor, is this not dependant on the display). I do however have seen that double tap to wake stops working after charging the phone (I'm able to reproduce the behaviour repeatedly)? It will after a few hours of work just magically return to normal?
Proximity sensor goes through stages where it does not work either. I can't for certain say this happens after every charge but maybe it's just a coincidence that this happened after my last charge.
Some notification sounds do not sound at all, it seems to only happen when the display is turned off (or when the device is in standby?). Notifications including sounds such as locking and unlocking the phone aren't always played.
The screen does not turn on sometimes when and if a notification comes through (they do not always sound as in point 3 above).
Hey Cortana performance is terrible, it just doesn't work if the phone is not unlocked.
Gestures Beta has never worked on my Lumia 930, albeit a beta, I never have had any problems with it on my Lumia 920.
Things I consider to be the culprit:
There are so many issues with my device while it is in standby, that it seems to me that it might be a firmware problem? I can't image how being in low power mode would affect the device sensors (unless there is some kind of voltage drop in standby and the device's sensors are unable to function). Unsure why it seems to be fine when the device is unlocked.
I can't explain what charging does to double tap to wake, but the fact that this happens after every charge leads me to believe there is something here.
Things I have tried:
Pressing right hand corner of screen for double tap to wake. Did not help (also saw somebody going on about the phone bending in another post, my device is in a hard cover and the 930 has Gorilla glass 3, not sure it will bend at all).
Hard reset and reload firmware. Did not help (Currently running Denim).
Anyone experiencing the same problems and any solutions? I came here after being directed by Microsoft Mobile's facebook page. They don't seems to think posting my problems on facebook is a good idea. Honestly, this is my second Lumia 930 and after reading up on all the issues with the double tap to wake have a came to one conclusion: The build quality of this device is terrible.
Thank you for your time.
Jaco

Answer 1

Here's an update.
In frustration I tried pressing harder in the right hand corner, and if course that solves the issues (Lovely design flaw this). Although only temporarily and I still don't know how the charging is capable of affecting this at all.
My suggestion to Microsoft would be to allow in the next firmware update to allow users to disable this sensor. It seems that this sensor (or the light sensor next to it, who knows) is used to determine if the device is allowed to "Unlock" using double tap to wake. If this is the case, the device will simply ignore it when you tap on the screen (at the cost of somehow waking up in your pocket, a small price to pay)?
Anyhow, anyone's take on this?