Session Drummer 3 problem...Any help much appreciated! Deadlines to hit

 I get that too often, too! I can only offer my novice workarounds:
1. It seems to occur worst when I insert certain effects - notably the ones I wanted X1 for in the first place (e.g. LP64_EQ_64, etc.) - so I either don't use the respective effect (however, the problem sometimes seems to remain even after deleting the 'offender' from the effects bin, so knowing in advance which effects not to use seems to be the bet). Or, I bounce the MIDI to audio and then use the effect.
2. As the CakewalkSoundCenter soft synth doesn't seem to randomly drop hits, I'm resorting to using that instead of Session Drummer
... all of this makes me angry that I spent the money on X1! I suppose a patch would solve the problems?

Right. The SD 3 kit you're using may not be mapped to the notes in your MIDI track.
Open the PRV and click on the drum names on the left. The ones that make noise are the samples in the kit. If, for instance, the snare isn't sounding when you click it, you can drag that entire line of notes to the line that does sound when you click it.
You may ne using note C#3 for the snare in your MIDI track, but the SD 3 kit may use E#3 for the snare.

I removed all effects and busses from the track, recopies as midi and no dice so far. I also changed the "vary with pulse level" in audiosnap back to the constant level setting, and that was no help unfortunately either. the search continues!

Just a follow up here for everyone, i've determined this as coming down to a bitbridge error. In the project I'm currently working out of I had 32 bit plug ins running (my comp/sonar is 64) and session drummer 3 was acting up and leaving out hits. I opened a different song from this band that is yet to have any mixing done (i.e. no 32 bit plugs active), and session drummer 3 seems to be working fine. Looks like what we'll have to do is hit session drummer first, print to audio tracks, and then continue using our 32 bit plugins (until we buy 64 bit versions). Thanks for reading and hopefully this helps other posters in the future. If anyone has tips on printing SD3 to audio tracks please contact me or reply here, thanks!