I've tried pause protection, disable protection, shut down protection and it doesn't help. I can't disable anymore of the program as far as I can see! I can't stop it's service but I guess that's by design.
I have to actually uninstall Emsisoft to be able to load this game otherwise it crashes after the logo. It silently closes writing an exception to event viewer.
This isn't a new issue, it's done this since the release of the games demo last year but I just got the full version of the game so I was more motivated to figure out how to make it work!!
Game demo here if you want to give it a go: https://www.microsoft.com/en-gb/store/p/forza-horizon-3-demo/9nblggh52th6 (Windows 10 only I think)
Let me know if there's any further info I can provide. I have the event view log entry for instance but I suspect this would be more useful to Microsoft than yourselves and their answer is just to shut down the AV.