I have had this exact problem, and honestly, I'm happy to see I'm not the only one. I needed to finish a quilt for a Christmas craft show, with noone able to help me with the BSR. I just did manual free motion quilting the old fashioned way because I was under time pressure, The result was pretty great, and I don't feel much need for bsr anymore.
That being said, I wrote an e-mail to Benina USA and the reply was that it might have to do with the spring in the actual foot being too soft. My dealer hasn't changed it for me because they say it works fine for them at the shop. (Of course they probably use it for 2 minutes, to my 3 or 4 hours...), but maybe this little note would help.