The latest non-Steam patch is Title Update 1.8 which can be installed through the launcher or downloaded manually from Ubisoft's servers. The Steam version already has this patch.
Title Update 1.2 will lock the resolution to 720p. Patching to Title Update 1.4 resolves a lot of video resolution problems, and enables the game to be played in most resolutions and in Eyefinity set ups.
Any time you connect to a host with a different patch, you will be booted within 10–15 seconds of connecting. This is because the Steam version of the game is different to other multiplayer hosts or clients.
Check that no other network adapters are enabled. Adapters such as VPN, VirtualBox, and others may cause conflict. In the event that multiple are present, disable all but the one your intend to use and the issue should be resolved. Alternatively, you can attempt to change the priority for the network adapter.
Whilst the keyboard and mouse may be selectable within the game menu, but does not work in the game. Uninstalling the drivers for any installed gamepads fixes for some people.
Disable Ambient Occlusion in graphics options. Due to poor optimization, the effect is extraordinarily resource-intensive.