To work with Errai smoothly, JRebel needs some framework-specific integration to react correctly on the changes related to CDI or any other changes that might affect the metadata.
Do you have the sample application code available online (e.g. github)? Please send the question to JRebel tech. support and the guys can take a look on it then.
Errai integration was started but since not many users requested it yet the work somewhat staled.