My FIL often has efficiency issues with his AiO system and a friend of mine had similar issues to the point where he built himself a cooler mash tun to use with his. I don't know what the issue is, but you can pretty easily solve it by purchasing an extra pound of base malt for a few bucks. At the homebrew scale this isn't breaking the bank (like it would be a commercial brewery making 100s of bbls).
You can dump the oxidized portion, or add some vinegar mother and try to make it into wine vinegar. I'd just let that stuff go and enjoy the bottles that turned out well.
Take an actual gravity sample with degassed beer using a hydrometer. Your RAPT pill may have krausen crud stuck to it throwing off the reading. My conclusion for these sorts of devices is that they're useful for monitoring temp and letting you know when your fermentation is completed but the measurement of FG is probably inaccurate.
I think he's saying the dryer pieces themselves are stackable for storage when not in use, not that you should stack multiple carboys on top of each other using them.
They probably grow better there, but that doesn't mean they won't grow elsewhere.
Hops grow better in northern latitudes (within reason), they generally need longer summer days in order to produce flowers. People have successfully grown hops in Scandinavian countries (and not just southern Denmark). You probably can't grow them in Svalbard tho.
You should leave your bottles to condition for two weeks, that loud pop you heard after one day carbing with ale yeast is all the CO2 pressure in the neck of the bottle escaping instead of slowly dissolving back into the beer had you given it time.
I would wait for it to drop completely clear before racking it a second time.