I've scratched my head because of this odd behaviour. Sometimes the metronome just stops working, without obvious reason. No change on the settings or anything.The metronome doesn't stop working while playing or recording, but when I press play or record button (or keyboard shortcut).
 
When this happens, only way to get metronome to work, is to close the Sonar without saving the project. When Sonar is restarted, the metronome works just fine. And what is more confusing, if I happened to save the project while metronome didn't work, I can't get it to work when I load the project file.  

I've checked all the metronome settings, routings and busses, but it keeps quiet. 
Any thoughts?. 

where is the metronome routed to? aux track / metronome bus ? do meters indicate that this track or bus receives the metronome 'signal' (i.e. 1s and 0s) ?
 
have you tried disabling some of the new optimization options (e.g. allow arm changes ...)?

I've tried to send metronome to different places. Aux- / metronome- / master bus etc. No, there isn't any action on the meters. Midi metronome seems to be working, but audio metronome doesn't. 

I just got the metronome working, on one of those "corrupted" files. I clicked the FX button (bypass all audio effects) from control bar. It was active before I clicked it. The metronome still works if I press it again. Quite odd?.

I have to remember to press the same button, when metronome stops working next time. 

Man I don't know what made you click the FX button but I've been having the same problem it was driving me crazy,
thank you for that. I still think it's some kind of a glitch.

thank you for the FX trip. My metronome suddenly stopped working, and FX off/on turned it back on. Must be a bug.

I just created a new project with several buses and two audio tracks.  I enabled the metronome during record and I get no metronome.  The audio tracks play and record just fine, but I can't get a count in.  I tried the FX buttons trick, but it didn't work.  I assume the FX button being referred to is on the track being recorded.  Help!  Edit:  The FX button is the one at the top of the screen, not on the individual tracks.  When I switch it off and on the metronome now plays.  Weird bug.  Sorry for the redundant post.

For me, it was the FX button in the control bar near the top.
 
Block E on:
https://www.cakewalk.com/Documentation?product=SONAR&language=3&help=ControlBar.01.html
 
 

 
 
Thank you for this tip, I now have metronome again! This bug was driving me crazy! Damn cakewalk programmers...
I also experienced the part about getting metronome when closing project without saving, but losing it when saving project first.
 

It's a known bug that crops up now and then. Clicking the FX master button on the control bar usually fixes the problem. Cakewalk knew about it but was never able to track it down.