If we're supposed to have the flashback before the end of the arc it seems to be the best moment for it ; both Luffy and Kizaru are momentarily out, and Saturn (who seems responsible for Kuma's state) just appeared in front of Bonney.
I feel like this does seem like the right place for it cause yeah Bonney now has all of Kumas memories. But I figured it would happen after Kumas death
 
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