Half of an object looks weird when given transparency

As you can see in the attached photo, when I adjust the transparency on an object, half of it looks weird.

Have you ever seen a case like this?
It happens even when I control both the depthTest and depthWrite properties of the material.

If I open that gltf file in blender, it looks weird, and if I turn off Show Backface, the transparency works fine.

But when you view it in threejs, the transparency looks weird.

It’s hard to tell exactly what’s happening from just a screenshot, but alpha transparency is very sensitive to things like sort order, depth buffer settings, front/backside culling, etc.

Does material.side = DoubleSide vs FrontSide make a difference for you? Also see material.forceSinglePass.