The reason that Teensy LC was returning zero for R8 was because it has a 2-stop-bit mode and itís unnecessary to check that bit. Same goes for Teensy 3.5 and 3.6. This has been fixed in v3.2.2. The v4.0.0-alpha.1 has the fix for Teensy LC but not for Teensy 3.5 or 3.6.