Thanks Quentin R. yeah so what's weird is I ran a similar search size yesterday (with LI) which worked just fine.
The issue is about 20-30% of the list the LinkedIn URLs are not associated with a company on LinkedIn - therefore don't pull any results for people.
My way around it was to enrich the empty domains and then merge all the domains to use that instead and hopefully yield more results - but then we're running into the issue which we have here
So is this just something we'll have to chunk down a little? and do multiple searches for?