By any chance, did you turn on any of the settings under General/Accessibility/Increase Contrast, including Darken Colors? If so, turn them off and then check back to see if the toggle buttons have magically reappeared.
I know that makes no logical sense, but it worked in my case. The only reason that I figured this out is that as a last resort, I did a full restore of my iPad and set up as a new device. After doing that, I logged into my Apple/ iTunes account and went into Manage Subscriptions. The toggle buttons were back. Okay, I assumed that something had become corrupted in my old set ups, and as big of a PITA as the full restore as new was, I was happy to have the issue resolved. Then, I went about reactivating my preferred settings, including turning on the settings I described above. Later that day, I went back into Manage Subscriptions and the auto renewal toggle buttons were gone again! Imagine my frustration.
So I decided to undo any change I had made to my Settings since the restore (fortunately, it had only been a few changes at that point). In short, the difference was the Increase Transparency settings and, I believe in particular, Darken Colors. Since undoing that setting, the toggle buttons have been there and working as they should.
I know it makes no sense and it's obviously a bug in need of a fix, but hopefully this helps you!