In Syntorial V2 the Unison Spread knob jumps between values 0 and 1. This is by design. However, in version 2.0.007 and earlier, there's a bug in which a few lessons expect you to set it to the middle 0.5 value. This is a bug. If you experience this, simply update to the latest version:

Mac/Windows
  1. Log into your Online Account.
  2. Go to Downloads
  3. Download and install the latest version
iPad
  1. Download the latest version from the App Store;