Yes, look at the device detail page for your thermostat device, particularly the "Current States" section in the top right. What are the values for supportedThermostatModes and supportedThermostatFanModes? I'm guessing they are malformed JSON. To fix, you can try something like this with whichever attribute (or both) is in the wrong format (substituting the appropriate values for your device if they are different):
Depending on the driver you're using, a "Save Preferences" or "Configure" might also do this for you. If it's a community driver, the author may need to update it, but the above should work around the issue in any case.
