Metronome going silent - I've seen this numerous times in all X versions. Unfortunately I don't have any recipe to repro.
Probably there's a small bug in the GroovePlayer.

Suffered "silent metronome" in Platinum 2016.09...
I've never seen this before until yesterday I bought Platinum to replace my Professional....
Now metronome work perfectly in Pro but can't fix it in Platinum 201609...
 

jptrudel
Looks like the bug is still in 2016.09
Change anything in the Metronome and it goes silent.
Toggle Global FX and it's back.

Glad this I wasn't alone in this. And I worked with support on this, who ended up rebuilding my project to fix it. Although it's occurred in later projects . At least it looks like there's a workaround, "Toggle Global FX and it's back"

I had the opposite last night. I opened a project, it wasn't that old,, from June, and the metronome was playing. WTF.. I don't use the metronome much so most of my projects have no metronome buss and both the toggles in the tempo window were off which is my norm. This project would have never used the metronome.   I toggled them on and off and it still played-- real loudly too...
 
I had to open the options window and set the output to NONE. But why would it play when all the toggles were off, They were not ticked in the options window either.
I opened dozens of projects and only this one did this so I wrote it off as a normal quirky Sonarizim.   

Toggling FX worked for me too, thanks. I was scratching my head. I believe it stopped working when I set a loop and then a Punch section.