Hi!
To use Avada, you should wait for the future version of Avada which will be compatible with Polylang (I have been contacted by Avada authors and know they are preparing a new version which will solve the issue).
The current version of Avada believes that Polylang is WPML (because Polylang wants that) but then attempts to use WPML functions which do no exist in Polylang and thus breaks badly.