Unless there's something I'm missing, the init file and startup command I provided did the installation of those files for you into a temporary directory, so I thought that was the easiest self-contained path to reproducing. Let me assume you've run it once that way initially in order to fetch the packages (otherwise you can manually download the files if you want and adjust the paths in the below command line, but be aware that you need new enough versions of posframe that understands tty child frame). Then to get a "emacs -nw -Q" initialization you can use the attached test.el to do:

Then manually "eval" the remaining commands in test.el

(in another terminal) emacsclient -nw
Then invoke the child frame pop up: (C-x b and C-n to select *Messages* and RET). Now we're no longer in a minibuffer.
Switch back to the original emacs terminal
Invoke the child frame pop up: (C-x b and C-n to select *Messages* and RET). Now we're no longer in a minibuffer.
Swap to the emacsclient terminal, and note that the client is "hung".

 

I think this gives a specific enough recipe to minimally reproduce.