While entering a Japanese text in a shared Adobe XD prototype comment text field, it listens too aggressively to the "Enter key down" event. The Enter (Return) key is used by the Japanese input frontend to accept a conversion of the typed phonetic characters to the proper display characters. So pressing Enter key should only insert the composed phrase into the text field and allow further composition while the user is typing in Japanese.
I hope you can make an update so that an Enter key press posts the comment ONLY when a Japanese phrase is not currently being composed, as otherwise it is rather frustrating.
I'm not a programmer so maybe I'm being off the point, but it seems like you should not be listening to the key down event but to the actual carriage-return characters to be inserted into the text field.

I'm using Google Chrome 66.0.3359.181 on MacOS 10.12.6