I'm running HS3 on Linux, and have recently upgraded to HS3 Pro Edition (Linux) - which I know has been out for ages.

I've had a Javascript function running for years, working very well by calling the JSON API with a call like:

But now this call has started failing, returning an "Error, getting device status" to the client. In the HS3 log I get this error:
Problem serializing data for JSON request: An exception was thrown by the type initializer for Newtonsoft.Json.Utilities.ConvertUtils

And all other variant JSON calls now also fail. I have got the 'local login without password for JSON' set in Settings, so don't think it's an authorization problem, but I can't see what else it could be. The ASCII API version of a similar call works fine (though that one actually still requires authentication).

Has there been some change in the JSON API in this later version of HS3 ? Any other ideas as to what might be wrong ?