This is a really strange issue that I know is just some stupid button that I need to press or something but here it is:  I'm using some drum patterns in Session Drummer 3 on Producer 8.5 and seemingly at random, it will not play the pattern for a measure and then it will come back in.
 
For example, I've got a one-measure pattern loaded in, then I make a Groove Clip loop and stretch it out for eight bars. It will play the pattern for the first bar, then it won't play the second or third, then it will play the rest of the five bars just fine. Also, it happens on the same measures each time. I can see the MIDI info on the screen, but the stupid synth just won't play it. I tried freezing the track, and there is no audio in those measures that Session Drummer has decided to skip. I have tried deleting Session Drummer and re-inserting it with no luck. Still on the same measures there is a MIDI black hole that it won't register the information. If anybody has any suggestions I would appreciate it. I am in no way a power user with MIDI or Sonar so don't think you can insult my intelligence. Thanks.

Here is an update to my problem that might shed some light on what is going on. I've found that for those measures that don't play the MIDI info, if I zoom in a lot and slide that clip over just a few nanoseconds, then the clip will play fine. It's a work-around, as you can't really tell that it's not perfectly in time. But what that means is that Sonar (or Session Drummer) doesn't like that exact milisecond and won't play information then, but will if you move it over just a hair. Weird.

What that is implying is that the MIDI on and MIDI off data is happening at the exact same moment and so the note won't play, Therefore there must be an overlapping loop??
 
Did you look in the event list? 

Johnny may well have a point.
 
Select all your hits and set them to a length of, say, 30 ticks BEFORE groove clipping them.

I'll look into the event list and see what's happening there. However, any midi info in those measures is not registering, whether it is a loop or just a lone clip. No matter what I put in those measures, it won't play the info at the exact start of the measure, but move it over a bit, and it will. It is very frustrating to try to put in some drums and have it drop out randomly for no reason whatsoever. I'm going to play around with it a bit longer but I'm close to the point of just forgetting about session drummer 3 and finding another source for drums. 

Have you tried adjusting the buffers in Edit > Preferences > MIDI > Playback and Recording in the Playback section "Prepare using nnn Millisecond Buffers"? nnn should be 500 or higher.

After you've stretched the initial groove-clip out, try Bouncing the entire track to CLIP.
 
Now go into the PRV and see what you've got

scook
Have you tried adjusting the buffers in Edit > Preferences > MIDI > Playback and Recording in the Playback section "Prepare using nnn Millisecond Buffers"? nnn should be 500 or higher.

It was set to 500 already but I upped it to 600. No change. 
 
Another weird clue: I was trying to use a pattern in the Smart Loops/Straight Hard Rock folder that said it was eight bars. When I previewed it, it was eight bars. When I recorded it via midi into the track I was working on it was only seven bars. It left off the first bar for some reason. I tried multiple things to try to get it to play all eight bars with no joy. Oh well, the step sequencer does work as intended so I'm trying to use those. It's a shame I can't play those midi patterns in the step sequencer, which for some idiotic reason only can see .ssp files. Is there a way to play the midi patterns (steven slate/groove monkee/smart loops) in the step sequencer?