I have this issue as well and posted the details of my Mini PC I set up to be my Big Box emulation PC exclusively in the ticket.
I was just wondering, did anyone figure out a workaround or method by now to have the startup video play at least more reliable at the start of Big Box, particularly after a fresh boot of Windows? My goal is to keep Windows hidden as well as possible and have a kind of ultimate Super NES Mini experience, however not with Big Box replacing the Windows Shell (at least yet), so I replaced the Windows logo at the Windows loading screen with a Big Box logo, set a Big Box wallpaper at login screen and desktop wallpaper, a Big Box logo as the user logo, the user called Big Box, the desktop is completely hidden and the taskbar hidden by default.
I tried different methods, putting a shortcut of Big Box into the users startup folder and the Task Scheduler with various settings (with and without highest priority, with or without a delay), but it always works about 4 out of 10 times. When closed and launched again manually from the start menu it works most of the time (maybe 9 out of 10 times), however this is of course no fun, I just want to push the power button of the Mini PC, enjoy the startup video and have my controller already in my hands and my friends be impressed 😉
So anything someone figured out by now as a temporary workaround? Or since it is three months later now any news about a fix and a guess when it might be available maybe in a bete release, since I really care about getting this to work this would be a reason for me to test my luck and switch to the beta releases 😄