Unblocking non-https traffic on port 443 for remote access apps

I was using RemotePC for access to computers at other locations, but after update to FortiOS 6.0.2 the apps stop of working.

I downgrade but still I have problems with them, I try use other remote access app Splashtop and the same results.

The support said this

Splashtop Business app and streamer both do support proxy configuration. But one caveat is our data format for the remote session traffic is NOT standard HTTPS, which some proxies have issue with. (Our session traffic is an AES-encrypted TCP stream sent over port 443, not standard HTTPS format.)

The suggest the port 443 needs to be open, including non-ssl traffic. This is a bad idea for the security?

How can make this apps work with the Fortigate 50E that I have.

Thanks

Karl