So I am not sure I have outlined the subject well. The problem I have is when I drag a Midi Beat from Addictive drums 2 into the timeline Midi track for addictive drums, the first clip plays properly but if I copy it or ctrl click and drag a copy next to it, the second clip drops or doesn't play a snare or kick close to the end of the clip or sometimes the beginning of the next clip. This happens with all subsequent clips on the timeline. I have tried copying and pasting, drag to copy, dragging a new clip from addictive drums. I have made sure the clips do not overlap and no hidden notes are there. The only resolution I can find is to freeze the addictive drums synth and low and behold all of the notes are playing properly. This is a pain because then I cannot edit the drum track. Has anyone seen or run into something like this?
 
Sonar Platinum fully updated, Addictive drums 2, Focusrite 6i6 I/O, Windows 10

try increasing the "Prepare Using nnn Millisecond Buffers" in Preferences > MIDI > Playback and Recording from 250 to 500 or 750

What are you MIDI prepare buffers set to the default is 250 I found they are better set to 500

Preferences > MIDI > Playback and Recording > Playback Prepare using nnn millisecond Buffers.

Not necessarily related - but I had found that some intensive VSTi ( In my case NI Battery ) Would drop notes if their durations were extremely short. If I have durations less than 10 or so PPQ then I increased them and everything would play nicely.