Hops . Global shortage of certain varieties so may have had to change hops due to lack of supply / cost of supply. More likely they still use a certain hop ( Citra / Simcoe / Nelson Sauvign) just less of it and blend in another strain to boost the flavour.
Brewdog got an awful lot of column inches by pissing people off. They started with the Portman group , the group that oversees alcohol awareness by brewing ridiculously strong beer , 20% + ABV . Then got told off , asked not too by PG , then used this to winge and cry about it in the national press.
Then the whole ‘we hate camra’ campaign started and they helped with an alternnative craft beer festival in London at the same time as the GBBF. This got them more ngative press, and more column inches.
They dont brew great beer. IMO its mediocre at best . There are thousands of better beers out there that do not get national listings as they are not marketed well enough ,or the owners simply choose not to go down that road.
They do some inovative technical brewing which interets me, and are big enough to be able to shift say a Double Chocolate and Vanilla Stout for example , which would sell on the brand and packaging . Whereas if I brewed that we would be throwing it away as we dont have the clout to carry it off.