Sonar has been working well almost all the time, but sometimes, without any reason, Sonar starts to consume the entire CPU:
 



To solve this, only closing Sonar and restarting it with my current project.
Hence, the CPU normalizes:
 


 
Leaving the "Plug-In Load Balancing" option checked or unchecked makes no difference:
 


Someone would know how to solve this?

when you press the 'E' key does it stop?
 
E bypasses all plugins.
 
If that does it, try bypassing different fx until you find the offender.
 
Are you using Synths? Sometimes I push the processor level with synths. I'm not sure what would do that with the playback stopped. I would think if playback is stopped and it's still redlining, you might have input echo enabled and be routing your audio into something heavy for your system.

I'll try to bypass any plugin or fx next time. Thanks.
But from what I see, there is no other way to solve this problem other than closing Sonar, right?

Global bypass may well stop the excessive CPU consumption.
 
What happens next, when you subsequently re-enable the effects, will be telling. If you're lucky, when you undo the global bypass the problem will return. If that happens, start removing plugins one-by-one until you've identified the culprit. If you're unlucky, the CPU usage will settle down after re-enabling all plugins, making it much harder to figure out which one was going nuts.
 
This may seem like too much trouble, compared to just restarting SONAR to make the problem go away. However, you're eventually going to want to know which plugin is giving you grief so you can avoid using it in the future.

i have the same issue and it is usually a cakewalk plugin 

It happened again, in the same project. 
Suddenly, Sonar starts to take up too much CPU (and of course Audio Dropouts occur).
But unfortunately, this sudden CPU consumption by Sonar continues even by clicking on "Bypass All Audio Effects". So this does not seem to be caused by plugins, or the Bypass button does not completely disable these plugins.
Is there any other way to check what might be causing this bad behavior of Sonar?

Bypassing effects does not affect soft synth. One way to check if the problem is soft synth related is disconnect the synths. When the synth rack is docked with the browser the option is in the "Synth Settings Menu." When docked in the multidock or floating each synth has a power button on the left side in the rack. For more see https://www.cakewalk.com/Documentation?product=SONAR&language=3&help=Browser.11.html
 
 

scook
Bypassing effects does not affect soft synth. One way to check if the problem is soft synth related is disconnect the synths. When the synth rack is docked with the browser the option is in the "Synth Settings Menu." When docked in the multidock or floating each synth has a power button on the left side in the rack. For more see https://www.cakewalk.com/Documentation?product=SONAR&language=3&help=Browser.11.html
 

Thanks, the problem was really the synths.
I'm using 23 instances of Kontakt, in a massive orchestral template.
But disconnecting the first instances, the CPU has returned to normal. And even reconnecting these first instances, the CPU has no more overhead.
So, the problem is in the synth and not in Sonar, right? Or is Sonar still guilty?

It does suggest Kontakt or whatever Kontakt is running. I do not use Kontakt but would suspect any 3rd party libraries first.

I do not have Kontakt... if that happens again, can you somehow see in Kontakt incoming MIDI activity?
Also, check unintended VSTi MIDI outputs (check what is available for any MIDI track input, all VSTs with output enabled will be listed there).
Does any track has MIDI echo enabled (can be if "auto" echo is used)? And if yes, does the problem still there once all echos are disabled?
I mean if there is some "MIDI loop" (unintentional/Sonar MIDI routing bug/etc), that can "activate" all your instances producing heavy load.
 
Have you already tried stop/start Audio Engine button as a possible quick workaround?