When switching councils a Scout’s membership number changes. This affects identifying the proper advancement record in Scoutbook.
A unit Scoutbook Admin can either use the transfer tool to bring in a Scout’s record from a previous council then send an email to: email@example.com to remove the member ID from the current record for the Scout and retire that record. You will then have to enter the current member ID for the Scout in the Scout’s old record and activate Advancement Sync for the Scout.
Add it manually or to have the Council update his advancements on their end and then they should sync into Scoutbook automatically.