to reproduce:

  emacs -Q -nw
    C-x C-f /-:<host>:<file>

stackdump & gdb backtrace attached

problem only seen with:
  emacs-27.2-1 windows7 cygwin-3.3.4-2

problem doesnt happen with:
  emacs-27.2-1 windows7 cygwin-3.3.3-1
  emacs-27.2-1 windows10 cygwin-3.3.4-2

hopefully someone knows significance of 10240 byte file/buffer in emacs/windows7/cygwin64-3.3.4-2