Thanks for the info,
 
I'm using the ASIO driver mode (Is this preferable?)
 
My Clock source in Sonar = 'Audio'
My Clock on the Apollo = Internal

Hi Bruce (tenfoot) I tried your suggestion but it didn't fix the playback speed for me :(, but powering off/on the Apollo does.

Do you have a pick in your clock source (in Sonar) to something that represents your Apollo?

Hi Dave (dwardzala)
 
No,  the Clock Source options in the DAW are :- Internal, SMTE/MTC, MIDI Sync and Audio.
 
 

I have just noticed that in Sonar Preferences_> Audio-> Sync and Caching under File system Playback and Record I/O buffer size  is set to 256 , and the Buffer size settings in my Apollo I/f was set to 512. So I have changed this to 256 to match the DAW and will see if this cures it.  

icu81b4
Hi Dave (dwardzala)
 
No,  the Clock Source options in the DAW are :- Internal, SMTE/MTC, MIDI Sync and Audio.
 
 

I was thinking you were referring to the Timing master.  Pretty sure Audio is correct for clock source.

also make sure your windows power mode is set to high performance VS. Power save.
your interface could be going in to power consumption mode and thus the reason a reset is temporarily solving your issue.
(Windows Power settings = in control panel)

Those settings your looking at are for syncing an external device, like another sequencer to Sonar, they have nothing to do with your recorded audio clock rate. That is set in the ASIO control panel for your interface and will show in the Tempo widget. 
 
When it speeds up does the music also play at a higher pitch?    This is important. 
If it doesn't then that's not the Sample rate causing issue. 
When your sample rate changes it's just like speeding up or slowing down a record or a tape. 
 
If this is not the case then only the Tempo set by Sonar could possibly change, And that only changes the rate that midi is played back, not the audio. 

I have had a similar problem in the past which has not happened for a while. However, when mine did it the sound would become distorted and slow right down - you didn't mention anything about distortion so not sure if it's related. It did this with two different Focusrite sound cards - Safire and Pro 40. It would be random and occasional. What version of Sonar are you using?

icu81b4
Hi Bruce (tenfoot) I tried your suggestion but it didn't fix the playback speed for me :(, but powering off/on the Apollo does.

It must be a different issue then Alan. As far as I can tell the dynamic arming issue is only with wasapi exclusive mode enabled.