I noticed this weekend that when you access the 4.5 sandbox https://sandbox.moodledemo.net/ which was recently upgraded to 4.5.1, you are prompted to upgrade as site admin from the interface on alternate hours... I am not sure but I have an idea there are two primary sites that alternate syncing with the live site? If that's the case then I suspect one of them needs checking.

The 4.4 sandbox seems to be OK