I've been using the latest version of Avast Internet Security (at least the latest version for Brazilian Portuguese) v 12.3.2280 and I'm also facing the same problem with Forza Horizon 3 in Widows 10 Pro 64bits Anniversary Update.
I have a PC with an i5 4690, 8GB DDR3 RAM and an AMD R9 280x with its latest driver 16.9.2 and the game crashes some seconds after the game is opened.
I tried uninstalling Avast and the game ran normally after that. I insisted reinstalling Avast to check if the problem stopped, with no luck.
At least if I set Avast for Passive Mode and then restart the PC, the game runs normally. It's still very risky to use an AV on passive mode though, so I expect a solution for this.