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 scout that signed up for a STEM pack in another council, but is primarily active in our pack. I see this error message “Scout’s Name” has created a new primary member id which is active in another unit “Scout’s Name” will remain on this roster until their council registrar completes their transfer process or their annual registration for this unit expires.
I have heard of a STEM lab unit type. I have not heard of a STEM pack unit type.
Can you log in to my.scouting and check your Member Manager roster? Based on what I can see, the BSA member number For Hugo in Scoutbook does not match the registration with your pack (primary).