Resolved
Resolved in: 3.0.2
Overview of the issue
This can happen if a theme or plugin is filtering the override_load_textdomain hook and always returns true (even if the translations for the domain have not been loaded).
Workaround
This will be fixed in the next release.
Meanwhile, you can edit the MO.php file found in the ../wp-content/plugins/wpml-string-translation/classes/MO/JustInTime/ folder.
On line 61, replace:
if ( ! $loaded ) {
With:
if ( ! isset( $GLOBALS['l10n'][ $this->domain ] ) || $GLOBALS['l10n'][ $this->domain ] instanceof self ) {