Japanese text repeats after entering punctuation like "。" or "」" and finalize the input, if it is entered in combination with characters (Hiragana) without any conversions to Kanji or Katakana. Please see the screen capture movie attached for a reference. It looks like it is fixed in Affinity Photo Beta, so it will probably be fixed in future Publisher releases. But just in case it gets missed!

Publisher Beta
MacBook Pro (13-inch, 2018) with Japanese keyboard
macOS 10.14.6 I hope this helps! publisher-beta-