First thing I did when I received my Virus TI2 Desktop was what I do with all my devices: Upgrade it to the latest OS version. But instead of having a great working machine after that, I'd always get hanging notes when playing patches that used Mono mode.
The error was somehow random, but repeatable in that it would manifest itself after at most one minute of playing a lead or bass sound with lots of legato notes. Most of the time it would happen within a couple of seconds when holding a note (like a drone bass note) and then playing a line above it, so the the sound would always drop back to the first played note. Interesting enough, the note that gets stuck was not that first note, but some other random note.
After downgrading to TI OS 5.0.8.0, I am no more experiencing any stuck or hanging notes when playing Mono mode patches.
System Info: Virus TI2 Desktop, TI OS 5.1.3.0, Mac OS X 10.11.5, MainStage 3.2.4, Ableton Live 9.6