Is Delay Compensation enabled? What numbers are you seeing regarding latency on the source track(s)? Could it be a plugin's latency is not being read correctly(which would cause incorrect compensation) or does the delay window show red(meaning its out of the range of compensation)? Assuming Delay Compensation is enabled, I would use the original audio as a reference and nudge(or SPOT) the new audio into the correct position.
What is the reason for this routing(IOW, is there a better way to reach the same goal)? What about using Track Commit(I can't remember if 12.8.1 had that feature)
