@davemaxwell FOG, I doubt, is the culprit. See FOG, while fast, doesn’t “break” things, not in the sense I think you’re thinking.
The Client might interrupt an otherwise normal post-imaging step, but it is not FOG in any form destroying the sysprep information. I’ve run into things as simple as the host is restarting due to hostname change or ad join (directly client related but not “FOG’s” fault persay), to AVG/Antivirus, to drivers causing the image to not load properly on “first boot”.