Brewdog are about marketing their brand not products. That’s what happens when you go corporate. Out of the 100 so beers, they’ve made 3 good ones, Punk, Pony & Elvis. Clockwork Tangerine is good, but not exactly groundbreaking.
Fermenting vessels especially plastic can warp over time, rendering the lid non air tight. I'd give it 2 more days, check the gravity again. Which Mangrove yeast incidently?
I totally agree, the fundamental idea of BIAB is a full volume no sparge mash. For an extra quids worth of grain you can avoid the pointless effort of sparging & increase your efficiency by quite a few points.
I should of added, the beer will clear but you will find it goes hazy once you bottle & chill it, it's what brewers call 'Chill haze'. Plenty of info out there on the subject. athumb..
If you're doing BIAB and just lifting the bag out, I wouldn't worry about a stuck mash, issues tend to arise when recirculating the wort. As @GerritT says, keep them at 5% or below.
Chances are it will be a hazy beer without the protofloc, you could fine it with isinglass/irishmoss or flavourless geleatine, but this won't prevent the small proteins floctulating (clump together). If your FG finishes at 1.010, you're looking at 3.7% abv.
Apple flavours in beer can come from fermenting too high, you say 18C, was that the room temp or the beer? Some of these yeasts that come with kits are sub standard. I brewed one of these years ago & TBH they’re pretty flavourless.