As of Houdini 17.5.308, the plugin settings are now saved to a file in your Unity project's root folder, just above the Assets/ folder, with the file name heu_settings.ini. The previous way of saving and loading from EditorPrefs has been removed. The new way means that each Unity project will have its own local plugin settings, instead of being shared across all Unity projects. The file can be checked into source control for team-wide shared settings, or ignored from source control to keep changes locally. Your current settings will be automatically moved to this file, so you shouldn't need to do anything.

Similarly session data is saved out to heu_session.txt. This doesn't really concern the user, as its strictly meant for the plugin to keep track of the existing Houdini session during play mode transitions and domain reloads (code refresh).

I keep getting a Dictionary-related assert (“an item with the same key has already been added”) after some period of time using Houdini, possibly after deleting the asset cache or possibly from running Unity while the License Administrator isn't running, unclear. It at least appears the problem is caused by the heu_session.txt file holding multiple or invalid sessions, and the way I seem to be able to fix it is to delete that is by clearing out the heu_session.txt file, closing Unity, re-opening, and creating a new a socket session.

Is that like… ok? I'm unclear what session data you're storing here, or if me having to wipe it out occasionally will corrupt any of my in-scene Houdini objects, etc.

Basically, if I'm not meant to touch that .txt file, this would be a critical bug that literally prevents me from working. So long as I can clear out that .txt manually when it happens, it's a minor annoyance that I can just shrug and work around quickly.