I too have been having issues with my rear bike since I bought the bike in May 2020. Several visits to the dealer where they have bled the brakes (3) used ‘racing’ brake fluid and the safety recall all failed to resolve the problem.
Finally, they agreed to change the complete ABS system………..what a difference! Not only does the rear bake work the front is significantly better too. I thought the front brake was good but now it’s awesome.
So now I am happy but I’ve got to thinking, I’ve been riding a bike weighing 1/3 ton with no rear brake and a below par front brake and lived to tell the tale. Lets hope no one out there ends up in a bad way because of this long standing fault