I am in the middle of a project which has been working fine. It's a mixture of recorded audio for vocals and guitar and plugins for other instruments (Xpand2, AD2, SI-Bass). I created a mix of it to listen to in the car which worked fine.
 
Yesterday I was experimenting with different plugins (SI-Bass, Xpand2) and also made a few other changes e.g. added LP EQ to a guitar track. I haven't changed the content of any MIDI tracks but now I have missing notes on playback for the bass, drums and synth tracks (the data for the notes is still there!). I have tried other previous projects which all work fine so why am I getting missing notes on these plugin instruments only for this project? Apart from SI-Bass I didn't add any new plugin instruments I just routed existing MIDI tracks to them.
 
Is there any log or report I can look at to see if I am stressing the system and if so how?
 
Thanks

Try modifying the "Prepare using *** millisecond buffers" in preferences/MIDI/Playback and Recording.

As a starting point, the old (pre-X1) default of 500ms works well for most projects. The new default of 250 is too low in a lot of cases. Using mastering plugins that require a lot of Plugin Delay Compensation (e.g. Cakewalk's own Linear Phase EQ and Multband Compressor) may require increasing the MIDI buffer even more, but you would usually have soft synths frozen by the time you're mastering.

I set it to 500ms and the problem has gone. Many thanks! Another setting I wasn't aware of.
 
I was using LP EQ on an Acoustic Guitar track for HP filtering. Probably a bit of overkill on reflection.
I probably need to get myself into more of a routine about which effects modules I use for various situations. i.e. individual tracks vs mastering etc. There is just so much to choose from I often find that I am spoilt for choice.
For example, in the past I always used the Sonitus effects, especially the reverb which is great but only recently discovered BReverb 2 ProChannel module which sounds even better to my ears. 
 
Thanks again

Yes, for HP filtering I will always turn to the Quad Curve EQ built into the Pro Channel.
 
It has a good variety of slopes, is CPU friendly and to my ears at least, doesn't colour the sound in any way.

Thanks Bristol_Jonesey I will try that in place of the LP EQ.