The "mysterious" comment I made was because this virtual audio driver is unknown to me. ..and that company's web site does not work to show product information on that product. No insult was intended. I was mostly trying to eliminate variables.
When did this problem first appear? What change in one or more of your systems produced the change in behavior? As I said, neither of my JRiver systems have any significant delay. The most I've seen with random clicking and fresh startup is about 3 seconds.
I notice that you, and the other person reporting, are using older machines. This shouldn't necessarily be a problem, but you are reporting bad behavior on a 14 year old Mac, which almost certainly is running a rather old version of OSX. If you are running MC30 on a Mac with an OS that is several major revisions old, that might be producing a behavior that most of us would not see.
My two test subjects are both M1 Macs and are running recent versions of Mac OS 11 and Mac OS 12.
The big thing here, in my opinion, is to locate a scenario (OS + hardware + audio device + JRiver version) that works. Then find the thing that makes it not work. Reading what you have written, I suspect that this might be a combination of MC30.<something> and an older version of Mac OS (version 10.X). But I'm just speculating based on available data.
Finally I should mention that I am just a customer. I do not have any relationship with JRiver. I do not speak for them. I am not employed by them. JRiver staff might have different advice or observations.
Best of luck.
Brian.