I wonder if it has a log somewhere to see what makes it fail. In 1903 pro (.53) it gets stuck on the loading splash screen for me, and it used to work in earlier insider builds. Defender is there, Edge is there, People is there as well.
Many times Sandbox gets stuck on loading screen for me when launching it for the first time. I have to close it, then it works after that. For now Sandbox seems to be pretty much a bit shaky. I am on 18885 now. I am always happy when it works. I hope it gets more stable in the future.
I have found that if you are going to remove anything, like defender, edge, or IE then run this previous to their removal, and don't remove any files or folders, just alter the registry, and use powershell to remove packages.