This is probably a dumb question, as I know little about British coinage of this era, but does this coin show signs of being struck on an already struck coin? I see a lot of extra lettering under BRITTANIA and some other extra detail, especially on the reverse.
On the contrary, that is an EXCELLENT question!
On the reverse, the incuse letters running under "BRITAN" are "GEORGIVS" running counterclockwise, and you can see an incuse "II" just under the shield.
I vertically flipped the image of the obverse to see how another coin might have caused an obverse brockage. Obverse brockages occur when the previously struck coin is not ejected and gets stuck to the lower die.
This planchet looks like it got a weak impression of the obverse design from an initial striking with a coin stuck in the lower die, then the stuck coin was ejected, and the planchet struck again normally. If someone has a different explanation, let us know.