Same problem here.. It just not override the standard startmenu. Start10 is running, but is broken/not show.
Was this a clean install of Start10?
If so did it prompt you for activation?
I ask because we have had reports of other .net using apps not working at all on that insider build of Windows so it is looking like Microsoft may have shipped it out with a bit of a bug. If it is activated the app itself is perfectly happy but the OS seems to have broken the bit that prompts you for that. Unfortunately these are the risks of using unfinished Microsoft software.
If you run Start10Config do you get the config window?