I wish they had put a kb article up about that. I havent had any issues...

Here is the relative content from the email I received from Cakewalk:
 
"Step Sequencer clips do not open correctly when a track is assigned to a drum map.  I'm hoping to get that addressed. In the meantime, avoid using drum maps with SS. Use the PRV with the drum pane in that scenario."
 
So, since then I have stopped using drum maps when sequencing with Step Sequencer.
 
Bob Bone
 
 

I seem to be in Bob's camp.  Swamptooth, can we do a quick test?  Can you open a quick test project, insert a drum program(maybe session drummer since we both have it), point the midi track's output to a drum map, open step sequencer, create a sample pattern, close SS, and then double click on the clip to see if the notes show up?  I'd like to try the exact same experiment as you to see if it's some other variable.
thanks.

Followed your test. The notes do not show up in the SS BUT, I can get the notes to appear in the empty SS by adding one more step. Click the drop down menu in the clip and select Step Sequencer.

Ok, thanks.  That actually doesn't work for me.  Or it might work once, but doesn't the next time.  If you subsequently close that ss window and double click on the clip again, do the notes appear or do you need to select SS from the drop down menu every time?

The behavior is consistent.
 
Double-clicking the loop will open an empty Step Sequencer. First time, every time.
 
In order to get SONAR to repopulate the empty Step Sequencer select it from the clip drop down. First time, every time.

I believe my suggestion was to double click the clip once which will open step sequencer, then wiith step sequencer open double click the same clip.

Yes, as long as the clip MIDI editor is Step Sequencer, double-clicking the clip twice will open and populate the Step Sequencer.

Saints be praised.  Both ways work.  Double clicking the clip again puts the notes into the SS window.  And selecting SS from the top right icon, after SS window is open, also populates the notes.  I'm ok with this one extra step.  I'll use the double clicking twice method.  it's unfortunate it doesn't just work like it did in 8.5, but it's close enough. 
Thanks everybody! Now back to the music.

See this...
 
http://forum.cakewalk.com/X3a-Step-Seq-Am-I-the-only-one-seeing-this-m2903727.aspx