Scene3D stuck waiting for lock in FBO compositing mode

I am using a Scene3D item in qml to put a 3d scene over a camera image. When I updated to 5.15 from 5.13 my app would freeze after loading the first screen. Eventually we figured out that if we took out the Scene3D the app would run, and if we switched the compositing mode to Underlay it would also work. The issue is in FBO mode. Unfortunately, we can't use the Underlay mode, since we need to put the 3D scene over the image.