Welcome! This forum has a treasure trove of great info – Scouters helping Scouters! Just a heads up, though - all content, information, and opinions shared on this forum are those of the author, not the BSA.
I can add that I had manually entered new scouts, and once processed by council they had the appearance of being duplicates, but in fact it was a duplication in their membership. The sync brings them in with youth membership entry. I removed that leaving the real and active unit membership and all was good.
Every other Scout merged when the sync happened except for these two because the registrar didn’t put the hyphen in their last name. Advancement had been recorded for both Scouts already so I was hoping just to see it merge. I’ve given up on support so I’m manually updating both Scouts and connecting their parent so we can move on.