In AC17, walls no longer mitre when connecting. Due to the new priority based collision technology.
You are using Profile is seems, are you using element level surface overrides?
If using element level surface overrides:
Also override ends. This is a quick way to match the textures also.
Alternatively, open the Profile Manager (via context menu - Edit Selected Complex Profile). Select the Fill in the editor and under "Components - Selected" check that the Surface is coming from the Building Material (the end surface you see is likely the Building Material surface).
Then check "Use Building Material" this will change the surface of the entire Wall to come now from the Building Material (not just the end). If this is not the desired Surface you then have the option to modify the Surface used on that Building Material directly. Depends what you need.
James Badcock
Graphisoft Senior Product Manager