Rather than voting to close and leaving the answer in comments, it’s worth posting it as an actual answer so that others with the problem see an answered question in search results, rather than an unanswered one 🙂
Copied from the comments:
restarting the computer and VS somehow fixed this issue, closing
Yes I’ve seen this issue before (where the NuGet module isn’t loaded)
This issue is on the NuGet issue tracker, though it’s closed (at the moment)