As of Rider 2017.3.1, the IDE is complaining about a number of errors related to attribute usage, such as:
Attribute 'UnityEngine.AddComponentMenu' is not valid on this declaration type. It is valid on 'Class' declarations only.
The code in question belongs to a 3rd party package I'm using within Unity. Unity, however, complains of no such errors. I can "Ignore Errors" for t hese, but this setting appears to disappear when Rider restarts. It also appears to make Rider significantly less stable.