Hi,

   When editing chinese-book.txt(in attachment), I use (C-x h) to select 
all,
   GNU Emacs 26.3 only shows "mark set", then I use M-w to copy, it stops
   working.

   I try this on both Linux Mint 20.2, Debian 11.3, same error.

   Please use GNU Emacs in you computer to test chinese-book.txt and debug.
   Thanks a lot, :-)

Best Regards,

Bruce