Firstly I am using Platinum however it should work the same.
 
Tried to trip it up but I can't reproduce it. Definitely consider using the 12 outputs in Session Drummer though so every percussion sound can be treated differently at mixing.
 
I'm sorry but perhaps some kits don't use the same MIDI assignment and the pads are triggering no sound. Consider the step sequencer like an old drum machine with pattern based parameters. If no sound is loaded or the MIDI number for the percussion sound it will produce the wrong or no sound.
 

Thanks for trying that. Both session drummer and si drum kit lose the drum program each time.  I can load the same program again or a different one and it will start working for a while but then the same thing happens.  It seems to be whenever I make a change to the settings use the step sequencer or drag any of the info in the track.  I also tried to make sure that the output of the instrument was lowered so it was not going into the red.  I was sitting down today to really try to get to grips with using the drums as I'm still learning to use Artist so it's a little frustrating. I may try reinstalling everything and see if that helps.

That sounds like a strange problem.  I don't think I've ever experienced something like that while using a plugin unless the Sonar audio engine was dropping out completely.  That usually only happens if I have my audio buffers set too low and it can't handle the load.  What kind of audio interface are you using and what are your driver settings?
 
The MIDI buffers issue would have been my other thought, but seems you have covered that one already.
 
I tried to reproduce it using SI Drums and Session Drummer.  All stable here on the latest release of Sonar 2017.04.

Hi I've been using the Boss GT 001 as an interface. I use this and sometimes I use a Steinberg.  I'm really not sure but it's something to do with midi and the set up.  I've had the same problem with a few different test projects today which I did as tests once the problem started but I just tried another one briefly.  I had checked all the preferences for the device and the last project was ok.  It was odd though as I've dabbled with the drums before with no problem.  It's perhaps one of those things an experienced user would know what was going on straight away if they could see all the settings etc .  The replies back have been all very helpful.  I'm going to have another go tomorrow.