I had the same problem, when I checked the plugin ...

# intellij

[Czar]

I had the same problem, when I checked the plugin it was of the 2017.3 flavor, so I just removed it and restarted, the embedded 2018 plugin worked after that. My suspicion is on Sync, I have sync plugins enabled and I'm always importing settings from previous version, one of those (or maybe both) is probably the culprit of the problem.