Anyone else noticed this? Sometimes I will loop a few bars for a long time...5 minutes or more....while I screw around trying to find a good synth sound for something. And after a while, Sonar starts dropping MIDI notes. At first I thought I might be a Native Instruments thing because the project I'm working on had Battery drums and a Reactor bass line, but now that I've changed the bass to Z3TA (thank you Vintage 70's and 80's expansion!), it's still happening. It's not too much of a disaster because if I stop and restart the loop the problem goes away (and sometimes I have to admit the dropped notes actually provide some musical variation) but I just wondered whether this was a known issue. 

YEP big issue! having you card in ASIO helps and less than 2.8 ms too. 1.5 and it should be ok. AND REMEMBER NO look ahead plugins like yea Sidechained compressors :(. Exactly what we all want our drums and bass running through

I wonder if it's the instances of the concrete limiter I have running. That's look ahead. 

ru looping while changing patches? if so, check the polyphony setting on patches that you switch to. sometimes if its 0 or 1 it can cause that effect.

It's not the part whose patch I am changing that drops notes, it's tracks that are already finished. They just progressively skip more and more notes until I have to stop and start again. Only happens while looping, not ordinary playback. 

I'm digging this thread up because I've just hit the same problem and wonder if anything has been said on this issue since last November.

If I loop a couple of measures containing four notes after maybe 30 seconds the first note drops out, followed by the others one at a time, in order, so that after a couple of minutes nothing's playing.

The event inspector shows the notes being played, the track meters show the notes being played, but my master bus only shows the notes that are getting through, then stops completely when there are no more notes.

I often loop a small section just to play with the effects. I don't think Sonar should throw my notes away like that.

If I stop playback and restart the process repeats itself.

what kind of driver settings are you using??

I don't think this is a midi buffer issue, but who knows. It was set to 250ms but changing that to 1000 didn't change anything.

The situation is just 4 trumpet notes using DimPro, maybe 2 seconds for the 4 of them, so it's pretty slow.

These are not random drop-outs. It's always the first note of the four that disappears, followed by the others, one at a time, in order, losing one very 30s to 1 minute or so.

The notes still seem to be happening as I can see them happening in the event list. Funny, I could swear the first time the meters before the master buss showed activity for the silenced notes, but now all the meters follow what I can hear.

Go into Settings->Metronome. Check the "playback" box. Setting the metronome to sound during playback solved looping issues for me (someone from Cakewalk pointed out this hack a while ago) but it might not work for everyone. Of course you can mute the metronome in its bus, just as long as it's set to trigger during playback. Give it a try. 

Thanks sharke ! That seems to have fixed it.

Interesting solution :-)