Defender scans seem to be crashing my entire server

I posted earlier today about the fact that my whole server, and not just my multisite, seemed to have crashed. I was unsure as to the cause, but I could see that the database server was crashing. This happened repeatedly all night, beginning at around 4 PM Atlantic Standard Time yesterday. When I was finally able to get into my dashboard for a few moments and disable Hummingbird, Defender, and Snapshots, the problems instantly ceased. I enabled Hummingbird again a few hours ago with no problem. I then reenabled Defender and ran a scan. The scan hung at 99.7% completed and my entire server--every site I run, whether related to my multisite or no--crashed, resulting in immediate notifications from Jetpack.

I don't know why this seems to be happening, but I am unable even to SSH or FTP into my site to disable my plugins. This is clearly a major problem. Huge, actually.