Plugins / css ediot crashes all my sites

I have a wp site at jonathanrundle.com/blog and when I try to add a plugin – any plugin – all other sites on the same server crash until the next day when they reappear with no effort on my part. The same thing just happened when I wanted to edit the theme’s footer. I went to customize, the first css loaded in the editor, then I clicked to edit the footer which was listed on the right and it crashed everything.

I have no idea what is going on. Anyone ever heard of this?

Theme problem? Crazy that all my sites, WP or not go down for awhile and then reappear.