https://twitter.com/TLAlexander/status/1569181219446980608
The 50mm headphone drivers were globally out of stock for a year so it is safe to assume the new drivers are from a different manufacturing batch. But my hope is that the problem lies in my headphone design, and the new and old drivers are roughly the same. I don't know anything about headphone design and seemingly got lucky with the old design, so if I need to adjust my new design that's not a big deal. But if the new drivers aren't performing like the old ones, I may not be able to fix things. So next step will be to swap drivers from the old and new headphones and see if the problem follows the drivers or the headphone design.
Images of the old design as well as the link to the onshape files on this git repo: