Should I get a second opinion on my Bass?

6 months ago I brought my Fender Jazz Bass to a small business luthier for its very first setup. I had been playing it right out of the box for a little over a year and I felt like it was about time I brought it in. I also wanted to put some flats on it. I stopped taking my guitars to guitar center a few years back and have been trying to find somewhere solid. I tried this new luthier last year and he did a good setup on my acoustic guitar so I thought I’d bring in my bass. He did the setup with the new flat wounds and damn it was sweet. Until a couple weeks later the open A string starts buzzing like a jackhammer if plucked to hard. Buzzing completely disappears when fretting a note. After some research and troubleshooting I came to the conclusion that it was probably a nut issue. Is this something he should have caught when setting up the bass initially? Eventually I contacted the luthier to bring up the problem and he told me to bring it back and he’ll check it out. He wasn’t defensive and he agreed it was likely a nut issue and said he would fix it. When I picked it up he said it was on the house for good will and future business. It’s been another few weeks and the buzzing is back. I can get around not playing the open string but it’s still frustrating. I’ve built a pretty decent relationship with the guy and it’s a convenient location but I think I might need a second opinion. Should I bring it back to him or get a second set of eyes on it? What would you do?