Why isn't my user dictionary syncing on Marshmallow?

[AC Question]

User dictionary is not syncing on Marshmallow

Even though I’ve turned on the dictionary sync ON on both my Nexus 4 and 6p [to my Gmail account], still the dictionary does not sync on my 6p. What could be the possible reasons?

 

[B. Diddy]

Welcome to Android Central! You're using Google keyboard? Both phones are logged into the same Google account? Go to Settings>Accounts-Google>[your account]​, and make sure App Data is turned on.