Dr. Kahan at the Center for Weight and Wellness has experience with former gastric bypass patients. He has an impressive bio and focuses on obesity, obesity policy, etc. I don't have any personal experience because it ended up being out of my price range. I'll be following for other recs since I'm still looking for the same thing.

https://centerforweightandwellness.com/about/meet-our-team/

I had gastric bypass surgery almost 20 years ago and maintained a fine weigh for many years, but in the last 5 have gained a lot back (by no means all, but I need to loose 75 to 100 pounds). I have been eating no /little carbs for many years and that stopped me from gaining for a long time, but I feel like I am gaining again. I am Looking for a weigh loss coach or center to help set me on a plan and coach me through to weight loss. Experience with clients who has gastric bypass in the past is a huge plus.