Welcome to the world of beta testing. Personally, unless I had a lot of time to experiment I would only install Windows 10 on a separate boot drive for testing so that my machine that I know is working well would be available with a simple reboot.
There are many people that have Windows 10 and After Effects works...
There are also millions of combinations of drivers, display adapters, motherboards, and programs that may cause conflicts with Windows machines. Again I say welcome to the world of beta testing. You have not provided enough information to even hazard a guess at what is causing the problem.
I upgraded a work PC to Windows 10 and it worked fine with Adobe, however when I upgraded my home PC to Windows 10 Pro AE CC 2015 (with all latest updates) hangs at the start screen, always stoping at "Loading Mediacore."
My system details are:
CPU = Intel Core i7 4770 @ 3.40GHz, Haswell 22nm Technology
RAM = 16.0GB Dual-Channel DDR3 @ 798MHz
Motherboard = Dell Inc. 073MMW (SOCKET 0)
Graphics = 1024MB NVIDIA Quadro K600 (NVIDIA)
My main suspect for the failure is the NVIDIA graphics driver. The office PC is running a GeForce card and it all works fine under Windows 10.
You can easily and quickly revert to a pervious Windows installation. Go to Start Menu, select Settings, select Update & Security, select Recovery and there should be a Go Back To option. It took me a few minutes to revert back to my old Windows 7 Pro and everything is now working fine. Be warned this option will only be there for 1 month following an upgrade, after that you can't revert.