Thanks, [USER=“922965”]Julian Vinet[/USER] - I tried this too.
Starting a project from scratch with the same datasmith import, it works. So I can rule out it’s not the origin, so yes it must be a cache issue then.
With the swarm agent, it says cache cleared and revalidated but the crash remains.
Oh well, not a big deal as can just use GPU lightmass on new projects. Hope it helps anyone else in future.