Would you mind trying the following steps to see if that helps:

1. In Rider go to Settings | Build, Execution, Deployment and set MSBuild version to the one from Visual Studio installation;
2. Close Rider and delete the .idea folder;
3. Open solution in Rider and see if the issue still persists.
4. If the issue persists, please [report a bug][1] to our issue tracker.

Have a nice day! [1]: https://youtrack.jetbrains.com/newIssue?project=RIDER