Hi Stefano ,
i have the feeling that the problem with the "white page" is not relative with the symlink of scemd.log .
From my little experience with the DSM7 ,never happen to me .
More over, i had install more than 40times DSM on a lenovo PX4-400D, with different versions, just to check if that my system is stable and which version of DSM is more accurate
Also in most cases , i was just logged in to webpage to see that disks just wake up from hibernation .
Do you try to ping your machine when you have a blank page or Open Google chrome developer Console ?
Also check the nginx logs under /var/log/nginx/error.log