As I said before I've experienced the metronome going silent on me in versions of X1 before X1D. I haven't been in X1D much since the update, so I haven't seen this happen, yet.
Furthermore, when it happens it's radomly and there is no set of steps that I can report to reproduce the issue. The same was the case with SONAR 8.5. Yet, without steps to reproduce the problem, I think it's useless to log a bug report.
Bub mentioned a restart would get the metronome sounding again. I never tried that (I usually have to start a new project to get it sounding, again,) so I will give it a shot next time, but it's still a creativity smasher. I need the metronome the instant I need it, not a restart away.