I'm also a long time user of GadgetPack and I too have had this problem occasionally, but typing "Gad" and restarting Gadgetpack always seems to fix it where subsequent system starts reloads the gadgets. I haven't had the problem where that occurs evey time a boot process starts. Just to confirm it, I'm using "7 Sidebar v2,90" from "8 GadgetPack.net" where it's stored on my system in "C:/Program Files/Windows Sidebar". In that folder I have 2 "Applications", 8GadgetPack.exe Version 33 (64 bit) , and sidebar.exe. In my Task Manager The actual startup file is "sidebar.exe" with the path "C:\Program Files\Windows Sidebar\sidebar.exe". I checked in my Task Scheduler and there is no entry for that there.
It's been awhile since I installed this but I assume the installer is what puts the entries in the startup sequence. If it's part of the startup and it's not showing up initially, but will show up when you type "Gadgets", I'd check your startup logs to see what might be preventing it from starting initially. You can check your startup and shutdown logs via the event viewer using the procedure found at:
How to check the Shutdown and Startup Log in Windows 11/10.
Hope this helps....