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.
Last year as den leader I was able to submit the advancements for each scout without any issue.
Sometime last year, something happened to my account where I no longer showed as den leader and had no connection to my own kids, nor was I able to even see my pack.
Sounds like you did a training or something last year and created a Second BSA # for yourself - support is in a little limbo right now. What I would first suggest is go to my.scouting.org > Login (do not create account) > Click MENU top left > click Manage Member ID and see if it finds a second instance then merge them with the Primary one being the one that shows in Scoutbook
I would also first ask you unit if they see you in Scoutbook and see what BSA # it shows there. cause that is the one you want as it has connections to your Scouts probably
@MatthewSanchez - looking at it more - are you logging into Scoutbook with your gmail account as user name? if so try using your my.scouting.org username and password