mon (611000392b40) at <24,4> is not there!

[elunna]

(rr) bt
#0  __pthread_kill_implementation (no_tid=0, signo=6, threadid=140129761187776)
    at ./nptl/pthread_kill.c:44
#1  __pthread_kill_internal (signo=6, threadid=140129761187776)
    at ./nptl/pthread_kill.c:78
#2  __GI___pthread_kill (threadid=140129761187776, signo=signo@entry=6)
    at ./nptl/pthread_kill.c:89
#3  0x00007f728061a476 in __GI_raise (sig=sig@entry=6)
    at ../sysdeps/posix/raise.c:26
#4  0x00007f72806007f3 in __GI_abort () at ./stdlib/abort.c:79
#5  0x000055613b71ca26 in NH_abort () at end.c:236
#6  0x000055613b723b99 in panic (str=0x55613c2b6880 "%s") at end.c:803
#7  0x000055613bca725e in impossible (
    s=0x55613c267840 "mon (%s) at <%d,%d> is not there!") at pline.c:685
#8  0x000055613ba6f29e in mon_sanity_check () at mon.c:163
#9  0x000055613b526c18 in sanity_check () at cmd.c:5105
#10 0x000055613b41c16c in moveloop (resuming=0 '\000') at allmain.c:857
#11 0x000055613c139553 in main (argc=0, argv=0x7fff57d07448)

INFO:
(rr) p toplines
$2 = "The hell hound bites the weredemon.  (9 pts.)  (0 pts.)  (0 pts.)", '\000' <repeats 234 times>

#define PM_HELL_HOUND   68
(rr) p *mtmp
$3 = {nmon = 0x611000392c80, data = 0x55613c3a7bc0 <mons+7072>, m_id = 133212, 
  mnum = 68, cham = -1, movement = 12, m_lev = 17 '\021', malign = 0 '\000', 
  mx = 24 '\030', my = 4 '\004', mux = 24 '\030', muy = 5 '\005', mtrack = {{
      x = 0 '\000', y = 0 '\000'}, {x = 0 '\000', y = 0 '\000'}, {x = 0 '\000', 
      y = 0 '\000'}, {x = 0 '\000', y = 0 '\000'}}, mhp = 107, mhpmax = 107, 
  mappearance = 0, rider_id = 0, m_ap_type = 0 '\000', mtame = 0 '\000', 
  mintrinsics = 0, mextrinsics = 0, mspec_used = 0, seen_resistance = 0, 
  female = 1, minvis = 0, invis_blkd = 0, perminvis = 0, mcan = 0, mburied = 0, 
  mundetected = 0, mcansee = 1, mspeed = 0, permspeed = 0, mrevived = 0, 
  mcloned = 0, mavenge = 0, mflee = 0, mfleetim = 0, msleeping = 0, 
  mblinded = 0, mstun = 0, mfrozen = 0, mcanmove = 1, mconf = 0, mreflect = 0, 
  msick = 0, msickbyu = 0, mdiseased = 0, mdiseabyu = 0, mpeaceful = 0, 
  mtrapped = 0, mleashed = 0, uexp = 0, mtraitor = 0, isshk = 0, isminion = 0, 
  isgd = 0, ispriest = 0, isqldr = 0, iscerberus = 0, isvecna = 0, isgrund = 0, 
  iswiz = 0, wormno = 0, mwither_from_u = 0, mstonebyu = 0, mstone = 0, 
  mberserk = 0, mwither = 0 '\000', vuln_fire = 0 '\000', vuln_cold = 0 '\000', 
  vuln_elec = 0 '\000', vuln_acid = 0 '\000', mstrategy = 0, mtrapseen = 0, 
  mlstmv = 0, mspare1 = 0, minvent = 0x0, mw = 0x0, misc_worn_check = 0, 
  weapon_check = 0 '\000', meating = 0, msummoned = 0, msicktime = 0, 
  mdiseasetime = 0, mreflecttime = 0, mprotection = 0 '\000', 
  mprottime = 0 '\000', former_rank = {lev = 0, mnum = -1, female = 0 '\000'}, 
  mextra = 0x0}

A were demon attacked the player, summoned a hell hound. It looks like the hell hound was placed correctly, but then is just not found. All were on different squares.

Hellhound (24,4) Weredemon (23,5) Player (24,5)

Info on the weredemon

(rr) p *mtmp
$10 = {nmon = 0x611000393a40, data = 0x55613c3b7120 <mons+69888>, m_id = 133171, 
  mnum = 672, cham = -1, movement = 12, m_lev = 19 '\023', malign = 7 '\a', 
  mx = 23 '\027', my = 5 '\005', mux = 24 '\030', muy = 5 '\005', mtrack = {{
      x = 24 '\030', y = 5 '\005'}, {x = 24 '\030', y = 4 '\004'}, {
      x = 25 '\031', y = 5 '\005'}, {x = 25 '\031', y = 4 '\004'}}, mhp = 106, 
  mhpmax = 136, mappearance = 0, rider_id = 0, m_ap_type = 0 '\000', 
  mtame = 5 '\005', mintrinsics = 0, mextrinsics = 0, mspec_used = 0, 
  seen_resistance = 0, female = 1, minvis = 0, invis_blkd = 0, perminvis = 0, 
  mcan = 0, mburied = 0, mundetected = 0, mcansee = 1, mspeed = 0, 
  permspeed = 0, mrevived = 0, mcloned = 0, mavenge = 0, mflee = 0, 
  mfleetim = 0, msleeping = 0, mblinded = 0, mstun = 0, mfrozen = 0, 
  mcanmove = 1, mconf = 1, mreflect = 0, msick = 0, msickbyu = 0, mdiseased = 0, 
  mdiseabyu = 0, mpeaceful = 1, mtrapped = 0, mleashed = 0, uexp = 0, 
  mtraitor = 0, isshk = 0, isminion = 0, isgd = 0, ispriest = 0, isqldr = 0, 
  iscerberus = 0, isvecna = 0, isgrund = 0, iswiz = 0, wormno = 0, 
  mwither_from_u = 0, mstonebyu = 0, mstone = 0, mberserk = 0, 
  mwither = 0 '\000', vuln_fire = 0 '\000', vuln_cold = 0 '\000', 
  vuln_elec = 0 '\000', vuln_acid = 0 '\000', mstrategy = 0, mtrapseen = 0, 
  mlstmv = 114104, mspare1 = 0, minvent = 0x0, mw = 0x0, misc_worn_check = 0, 
  weapon_check = 0 '\000', meating = 0, msummoned = 0, msicktime = 0, 
  mdiseasetime = 0, mreflecttime = 0, mprotection = 0 '\000', 
  mprottime = 0 '\000', former_rank = {lev = 0, mnum = -1, female = 0 '\000'}, 
  mextra = 0x6060009f6f80}