It looks like Roku is aware of a possible issue when the “auto-adjust display refresh rate” is enabled. Please check to see if that is enable, and disable it. That should correct the sync issue in the interim. Also note, if you need to have that setting enabled (if you notice video stuttering), then seeking for a second during playback should also correct the audio sync.
To Disable the setting: https://support.roku.com/article/115012823268-how-do-i-change-the-display-refresh-rate-to-match-the-native-format-of-each-movie-video-or-tv-show-
