I think this should be the "m" variable in the assert:

(lldb) frame select 9

frame #9: 0x000000010020bab4 emacs`adjust_markers_for_insert(from=1,
from_byte=1, to=15403, to_byte=15413, before_markers=false) at insdel.c:294:
7

   291   adjust_suspend_auto_hscroll (from, to);

   292   for (m = BUF_MARKERS (current_buffer); m; m = m->next)

   293     {

-> 294       eassert (m->bytepos >= m->charpos

   295        && m->bytepos - m->charpos <= Z_BYTE - Z);

   296

   297       if (m->bytepos == from_byte)

(lldb) p *(struct Lisp_Marker *) m

(struct Lisp_Marker) $1158 = {

  header = (size = 4611686018477740032)

  buffer = 0x00000001026b2718

  need_adjustment = false

  insertion_type = true

  next = 0x00000001026f5f70

  charpos = 0

  bytepos = 11043

}