Have you played a lot of games through family share? On the Tools section of the account page it’s recommended to use the analyzer tool from SteamHunters to find those. It’ll give you a list of app IDs that you can paste into the form.
Without using that tool it’s not possible to retrieve them from the API after more than two weeks. Another issue could be that the license has expired (meaning you no longer have access to the shared games).
In terms of games we can see through the API right now your profile appears to be fully synced. So I’m guessing, it is down to the family shared games. Normal scans pick those up now (if played within the last 2 weeks), but we didn't start picking those up until around 2016-2017, so anything before that could be missing if you hadn't played the game since.
not a lot, just a few. again hard to say whats not there.
it isn't entirely practical to cross-reference with c.me or ASTATs, though that might ferret out a few culprits.
thank you for checking to see if it had fully scanned on your end.