I'm exporting using the AutoRigPro exporter. In Blender, the weights look fine (the first image). However, After auto-weighting to my rig, I needed to do some manual painting around the wrists to fix deform issues. Then on export to FBX I get the issue you see in the second image.
Any vertex I painted manually or modified in the slightest with the blur tool doesn't seem to export properly.
I checked and the bone I'm weighting to is the correct one, and is exported. The weights are normalized. There are no more than 4 weights per vertex. Any idea what's going on here and how to fix it?