Quick and dirty fix should be as follows.
In src/XF/AddOn/DataType/Phrase.php, find:
Code:
$existing = $this->finder()->where('title', $ids)->where('language_id', 0)->keyedBy('title')->fetch();
Replace with:
Code:
//$existing = $this->finder()->where('title', $ids)->where('language_id', 0)->keyedBy('title')->fetch();
In the same file, then find: (13 lines below)
Code:
$entity = $existing[$id] ?? $this->create();
Replace with:
Code:
$existingPhrase = $this->em->findOne('XF:phrase', [
'title' => $entry['title'],
'language_id' => 0
]);
$entity = $existingPhrase ?? $this->create();