Having difficulties in using Phonetic Guide in Word 365

Being a beginner to MS Word 365 (Chinese version), having trouble using new behavior of Phonetic Guide

Have been using MS Office 2003, 2016 for years. But with old PC retired, I started to use 365 at home PC while still using 2016 in working location

I have been learning Japanese language for 2 years, with a Word document to summarize content for revision. In it, I use Phonetic Guide to add Furigana

A weird behavior found in Word 365 of my PC is that, while I apply Phonetic Guide to a short sentence, Furigana was still provided, but in several cases, not just to Kanji only, it is applied to the Hiragana characters as well!

Hiragana in Japanese is pretty much similar to a-z letters in English. So, its behavior now is like puting an "a p p l e" as the Phonetic hint for an "apple" word in content, quite pretty wierd and un-necessary, not really helpful but also decrease the readibility

While I open the same document in Word 2016, I tried to remove Phonetic hint above the sentence, then I highlight-ed it and press Phonetic Guide again, the problem is gone! Word 2016 can behave normally on the same sentence that Phonetic hint is suggested for Kanji only

So my question would be

What's wrong with my Word 365?

Any option I selected wrongly and causing such behavior?

And, most important how would it be resumed?