I have no idea what happened (and it happened to me with Manjaro as well, but using gtk3-nocsd and “sierrabreeze” I didn’t care about the problem).
But this time, since I didn’t need it, I decided to remove it immediately and, however, I find the “basic” breeze window decoration as in the image: here .
Also, hoping that reinstalling the package would solve the problem: I don’t know why it is now double … with the second it is aesthetically ugly, with round edges and looks more like an Aurorae decoration than the real breeze … and same thing as a widget style : gives a second option, with the language in English and not in Italian (like the original and all the rest of the system).