Your .NET Core applications stopped instrumenting, is it possible that some require environment variables has been overwritten or something else is preventing from the New Relic Agent from profiling, we recommend following this Community Post, do let us know if you have gone through it already.
For .NET Core, you must configure your application to be monitored by setting the following
CORECLR_ENABLE_PROFILING=1, for other environment variables needed (which should be set with the latest version of the .NET), see this link.
Also, see our troubleshooting guide for app(s) that have stopped reporting data to APM.
FYI: We have seen cases where the app is .NET Core but it’s targeting the .NET Framework, see below Community Post which may not apply to you but it’s something to keep in mind.
Do let us know how you get on and also can you share the permalink of your app, please?