After the last Platinum update midi notes were skipping during playback and i adjusted the Milisecond Buffers from 250 to 750 and the skipping stopped.  Today I updated Sonar again and the skipping has started again. All the audio tracks playback is fine, but the bass and session drummer tracks, are skipping noted randomly. Any suggestions

Hi. Maybe try some numbers in between 250 and 750? I have mine set to 500 on my systems.
All the best. 

I messed around with the settings and it finally seems to work at 800 for both the bass and drums. I wonder what in the update caused the need to change this setting? makes me wonder if so many updates is a good thing. What else will it change?

I have had mine at 500 since (at least) X3, and have not had any problems with skipping notes. I do not recall hearing about any change in updates regarding this. But it has been mentioned earlier, that there is no one fits all solution to this setting. Maybe 800 is "your number".
Have you had problems with this earlier with big projects? It seems like it becomes an issue with bigger projects. 
All the best.

Any chance you've inserted one of the new LP Mastering plugins in the project? Linear phase processing requires a big look-ahead buffer, and the resulting Delay Compensation can cause trouble with MIDI buffering. I don't have a problem at 500ms unless I raise the 'Precision' to 'High' on one of these plugs. Running a very high ASIO buffer could also contribute to needing a higher MIDI buffer.

If the project that is skipping notes is a fast bpm, a higher midi buffer makes sense because the number designates a lookahead in milliseconds.