I don’t think you get more answers by reposting this… You can always bump a thread by adding further information or rephrasing the question.
You are talking about delay, what delay? You will need a better understanding about timing. Your mouse click happens on the message (GUI) thread vs. audio happens on the audio thread. The audio thread will not wait for things on the gui thread. So if e.g. some heavy painting or something else blocks the message thread, it takes some time until the audio thread knows, that there is something to play.
But this happens somewhere deep in your code and not at all in processBlock or similar places. It is impossible for anybody to know, hence no reply to your topic so far.
HTH