I think everyone can agree that 宵宮(よいみや) has 4 mora. But one side says it has 4 syllables because there are 4 vowels.
The other side says "Yoi" is similar to the かあ in 母さん and thus only have 3 syllables. https://ja.wikipedia.org/wiki/%E9%9F%B3%E7%AF%80#%E6%97%A5%E6%9C%AC%E8%AA%9E%E3%81%AE%E9%9F%B3%E7%AF%80
Which side is right here?