I had the same thing with my MacBook. Searching the internet shows that it might have to do with FileVault and not having an external keyboard/mouse connected. Do you use FileVault on you Mac?
For me the following sollution works:
- Go to System Preferences/Bluetooth/Advanced...
- When I saw the problem, in my settings there I only had the last option ("Allow Bluetooth devices to wake up this computer") enabled. Since I've switched each setting (so enabling both options about the "Open Bluetooth Setup Assistant at startup..." and disabling "Allow Bluetooth devices to wake up this computer"), I can simply boot my computer with a responding keyboard and trackpad.
(I'm still experimenting with these settings.)
I hope this helps you too.
Kind regards!