Emacs sometimes crashes on C-x 8 RET, ie. (insert-char).

Sorry, but I didn't find a way to reproduce this issue with emacs -Q.

This seems to be related to vertico-posframe-mode (which puts the
minibuffer in a separate child frame).  I can confirm that if I disable
vertico-posframe-mode, this problem disappears.

Attached are the system-generated crash report and a backtrace obtained
from LLDB.