Thanks for reaching out and welcome to the Bose Community Forums.
I am sorry about this issue you are having. Can I please ask, is your other test headset a U174 plug unit, or a dual plug? If you are able to find an aircraft that you can plug into with the U174, we could tell where the fault lies. But as there is Bluetooth involved, it may be a little harder to pinpoint without speaking with you further.
If you are unable to find another aircraft to test, I would ask that you give us a call to discuss this further. You can do this by clicking this link here, selecting your region, scrolling to the bottom of the page, and selecting contact us.