Rigging with automatic weights acting like with empty groups

The title says it all really! I have a character adapted from an FBX of a Daz figure.
I’ve tried to attach it to a rigify rig with automatic weights, but all the groups are at zero as if I’d selected empty groups. I had deleted all the groups that came with the FBX and applied all transforms prior to this.
Not sure why this is happening. It only affects the skin. The eyes, lashes, brows and mouth all work fine.
I’m using v4.4 in case that’s relevant.

Hi, there could be more then one reason for this. We need to see your file to be able to give you a more precise solution.