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 have a cub in Scoutbook (137366703) that recently joined my pack. This ID currently has advancement attached to it & is marked as advancement synced. It has been the only listing of this person in Scoutbook. During recharter, I noticed there were 2 IDs for this cub in my.scouting. After asking my registrar to merge the 2 IDs with the Scoutbook ID as the remaining, the other survived. So, this ID, although marked as synced, no longer has a corresponding ID in my.scouting.
The ID listed in my.scouting (13735216) has never filtered to Scoutbook & is now the only ID for this person in my.scouting. Both IDs continue to show on my recharter roster. Refreshing the roster does not remove the deleted ID. On my recharter, I have moved the Scoutbook ID to “remove from roster” so it will match scoutnet.
To add to the issue, this is a Lion Scout with an adult partner for each ID (137366704 & 13735217). My registrar did not attempt to combine these. Both are on the my.scouting roster & only -704 is in Scoutbook (attached to the -703 cub).