It shouldn't require a new app, no. I'll loop in one of our engineers who worked on the .NET Core Provider. My first thought is more that it'll be a version compatibility issue (we're using .NET Core at Raygun for some new sub-systems, and while it's been evolving, the version story is a bit of a challenge to deal with. Could be wrong that this is part of the issue -- I'll leave it with the expert!).
In the meantime, could you share:
- What version of .NET Core you're using
- How you've integrated Raygun
- Any other frameworks you're using