Need to resolve design flaw - With whom should I consult?

Lets say I'm manufacturing suspenders. These suspenders are being white labeled by about 4 different sellers and across the board, all one to two star reviewers are complaining that the stitching is coming loose after using for a week.

I've ordered these suspenders both from the competitors on Amazon and as well as a sample from the factory and have confirmed that this is in fact an issue.

I've been working with the manufacturer to customize this product for over a month now and refuse to pull the trigger until this issue is fixed.

The problem however is that I have no idea how to fix it. I had the manufacturer add a piece that I believed would resolve the problem, however, this proved to be a failure.

I believe the next step is to consult with someone who has experience designing this product.

Who do I reach out to? Is there some sort of textile engineer, seamstress, or clothing designer that would be the best to consult with?