I have a part named Dragon who is stubborn, silent, and hella intimidating. Even now that I know him better he’s still that way. It sounds like you’re making amazing strides at opening communication and fast, too. It took Dragon a bit longer to respond. My opinion— give this one time. Check in once in a while.
I met a “new” part 2 months ago and inspite of attempts to communicate only really saw communication happen yesterday, mostly with pictures instead of words. It was good. I had some questions answered. I have others I met over a year ago that still want nothing to do with communication, but my t tells me “slow is fast.” I am betting that your mysterious one will help your system out with understanding as time goes by.