I myself have recently had this issue happen from time to time. I found quitting Sonar and re opening made it go away. It was like my CPU was real busy but the meters show otherwise. 
And this was on a few bare bones projects that had almost nothing going on. 
I'd even open a new project and drop one audio track and it still would stall for a good 7 seconds. Ever action was delayed. It's not graphic in my case as I've always used the on board video. 
So not sure if it's related but I also wonder what it could be. Windows 10 is always my chief suspect.

I've experienced this occasionally. In my case, however, it always went away (nearly) by itself. I never new what caused it.
IIRC sometimes it stopped when I toggled Audio Engine on/off. Also, IIRC, it did have something to do with heavier softsynths or effects.

If you are using it, try turning auto-save off.

Not me for that very reason. 

This sounds like I/O buffer size in the (advanced/hidden) Sync and Caching tab in preferences.

I like kperry's thought. have you tried it? For whatever reason, it sounds like waves are always being retrieved from disk rather than memory buffer.

Sorry, I've been really busy and have not yet had time to try anything for a while. I will try to check some things out and report back when I can.

If you have the option of Allow Arm Changes During Playback/Record set in Edit > Preferences > Project - Record, it may be causing overhead, with the number of channels your device has. If this is your case, search for "allow arm" in Help for some helpful discussion of that.

bvideo: Don't we need that checked to be able to do punch ins?

KPerry: I believe my I/O buffer sizes are set to 64. What's recommended?