What does Enable/Disable Independent Voice Playback do?
If a part has more than one voice, it will route each voice to a different VST slot (thus allowing for example, one voice to play pizz and the other arco at the same time)
… and by so doing, increase the CPU load for playback. Considering the difficulties you are having with playback I suspect this may be at least a significant factor but I will leave it to more knowledgeable folks to comment further. Do you have many multiple-voice instruments with independent playback enabled? Does your playback improve if you disable independent voice playback on those instruments?
Thanks. I set it to Disable but unfortunately that did not help.