Wow. That was a strange update. Initially, I thought the phone was bootlooping because the installation seemed to stop and start twice. After that twinge of arrhythmia, the installation still seemed to take a heck of a long time. I walked away twice; I couldn't watch. Thankfully, the phone did reboot, but then instead of just finishing things up, it started Google Play in the background and apparently updated every app that was already targetting API 26 (at least that's what I'm assuming since I updated 22 apps before I even checked for the update): YouTube, Google Docs, a Substratum theme that I don't even use on the 6P, Nova launcher, Network Signal Pro and the Official TWRP app, which I also don't use on this phone).
Crazy.