I had a working WPMU site. I was working on it last night. In network admin I installed the 'snapshot' theme, and network enabled it.
Around the same time (I can't guarantee exactly) I noticed my site A,B,C stopped working. The sites return an empty page.
This is one of the sites (cloaked because I don't want tech support posts showing up in search engines)
The network admin worked. Site admin pages also returned an empty page. I kept clicking in network admin and doing stuff, it was all still fine. I disabled the 'snapshot' theme. Still nothing.
I went to sleep, woke up and even network admin now returned an empty page. I deleted the 'snapshot' theme folder to no avail. I don't know if there are logs that tell me what's wrong. I haven't changed any plugins around that time. I disabled a FB OG plugin many hours before the incident so I don't think it's responsible.
These network sites have been working and stable for several days. The only other change I was making at the time was creating a new slideshow with this plugin
However only 1 site uses it, so it should not affect the other site or the network admin site.
I found this page and followed its instructions to no avail.