mct-region buffer pops up but without updating completions while typing

Today I installed mct and played around with the new in-buffer completion feature. Elegent idea!

My problem is: i) no expected updating behavior after manually activate the completion. ii) error of C-p

Emacs 28.0.91. Arch

Debugger entered--Lisp error: (wrong-type-argument numberp nil) mct-previous-completion-or-quit() funcall-interactively(mct-previous-completion-or-quit) command-execute(mct-previous-completion-or-quit)