This is happening on dhcpcd-10.2.2 version.
What seems to happen here is racing between SIGTERM and REPLY6 handling.

And below is pmd full back trace.

Core was generated by `dhcpcd: port0 [ip4] [ip6] '.
Program terminated with signal SIGSEGV, Segmentation fault.
#0 dhcp6_delegate_prefix (ifp=0x558af285e0) at dhcp6.c:3029
3029 dhcp6.c: No such file or directory.
(gdb) bt
#0 dhcp6_delegate_prefix (ifp=0x558af285e0) at dhcp6.c:3029
#1 dhcp6_bind (ifp=ifp@entry=0x558af285e0, op=op@entry=0x558691f960 "REPLY6", sfrom=sfrom@entry=0x7fe1779ac0 "fe80::5074:f2ff:feb1:a87f ") at dhcp6.c:3402
#2 0x000000558690e610 in dhcp6_recvif (len=, r=0x7fe1779cc0, sfrom=0x7fe1779ac0 "fe80::5074:f2ff:feb1:a87f ", ifp=) at dhcp6.c:3748
#3 dhcp6_recvmsg (ctx=, msg=, ia=ia@entry=0x0) at dhcp6.c:3886
#4 0x00000055869149b0 in ps_inet_dispatch (arg=, psm=, msg=) at privsep-inet.c:337
#5 0x00000055869118cc in ps_recvpsmsg (ctx=0x7fe1789e18, fd=, events=, callback=callback@entry=0x55869125b4 <ps_root_dispatchcb>, cbctx=0x7fe1789e18) at privsep.c:1181
#6 0x0000005586912434 in ps_root_dispatch (arg=, events=) at privsep-root.c:850
#7 0x00000055868e4b54 in eloop_run_ppoll (signals=0x7fe178a058, ts=, eloop=0x558af17810) at eloop.c:1106
#8 eloop_start (eloop=0x558af17810, signals=signals@entry=0x7fe178a058) at eloop.c:1228
#9 0x00000055868dda74 in main (argc=, argv=, envp=) at dhcpcd.c:2648

(gdb) bt full
#0 dhcp6_delegate_prefix (ifp=0x558af285e0) at dhcp6.c:3029
j =
--Type for more, q to quit, c to continue without paging--
ifo = 0x558af28910
state = 0x0
k =
ia =
carrier_warned =
ap =
i =
sla =
ifd =
ifo =
state =
ap =
i =
j =
k =
ia =
sla =
ifd =
carrier_warned =
loglevel =
s =
#1 dhcp6_bind (ifp=ifp@entry=0x558af285e0, op=op@entry=0x558691f960 "REPLY6", sfrom=sfrom@entry=0x7fe1779ac0 "fe80::5074:f2ff:feb1:a87f ") at dhcp6.c:3402
state = 0x558af03b50
timedout = false
confirmed =
ia =
loglevel = 6
now = {tv_sec = 1345, tv_nsec = 896085470}
#2 0x000000558690e610 in dhcp6_recvif (len=, r=0x7fe1779cc0, sfrom=0x7fe1779ac0 "fe80::5074:f2ff:feb1:a87f ", ifp=) at dhcp6.c:3748
ctx =
preference = 0 '\000'
ol = 55461
auth_len = 24489
op = 0x558691f960 "REPLY6"
state = 0x558af03b50
opt =
ifo =
auth =
i =
o =
--Type for more, q to quit, c to continue without paging--
valid_op = true
ctx =
i =
op =
state =
o =
preference =
ol =
opt =
ifo =
valid_op =
auth =
auth_len =
func = "dhcp6_recvif"
ia =
#3 dhcp6_recvmsg (ctx=, msg=, ia=ia@entry=0x0) at dhcp6.c:3886
from =
len =
sfrom = "fe80::5074:f2ff:feb1:a87f \000\000\000\000\000\000\000\000\001\000\000\000\000\000\000\000\215\000\000\000\000"
ifp =
r = 0x7fe1779cc0
state =
o =
ol = 16
func = "dhcp6_recvmsg"
duid = "\030\236x\341\177\000\000\000\003\004@\240\000\001Q\200\000\000\070@\000\000\000\000\375\245d6\323\307\000d\000\000\000\000\000\000\000\000fe80::5074:f2ff:feb1:a87f \000\242w\341\177\000\000\000\020\211\362\212U\000\000\000\020\211\363\212U\000\000\000\300\234w\341\177\000\000\000\001\000\000\000\000\000\000\000\000\001", '\000' <repeats 22 times>, "\001"
dp =
duid_len =
#4 0x00000055869149b0 in ps_inet_dispatch (arg=, psm=, msg=) at privsep-inet.c:337
ctx =
#5 0x00000055869118cc in ps_recvpsmsg (ctx=0x7fe1789e18, fd=, events=, callback=callback@entry=0x55869125b4 <ps_root_dispatchcb>, cbctx=0x7fe1789e18) at privsep.c:1181
psm = <error reading variable psm (value of type `ps_msg' requires 65760 bytes, which is more than max-value-size)>
len = 246
dlen = 182
iov = {{iov_base = 0x7fe1779cc0, iov_len = 110}}
msg = {msg_name = 0x7fe1779c78, msg_namelen = 28, msg_iov = 0x7fe1779c28, msg_iovlen = 1, msg_control = 0x7fe1779c98, msg_controllen = 40, msg_flags = 0}
stop = false
func = "ps_recvpsmsg"
#6 0x0000005586912434 in ps_root_dispatch (arg=, events=) at privsep-root.c:850
--Type for more, q to quit, c to continue without paging--
ctx =
func = "ps_root_dispatch"
#7 0x00000055868e4b54 in eloop_run_ppoll (signals=0x7fe178a058, ts=, eloop=0x558af17810) at eloop.c:1106
nn = 0
e = 0x558af22090
n =
pfd =
events =
n =
nn =
e =
pfd =
events =
#8 eloop_start (eloop=0x558af17810, signals=signals@entry=0x7fe178a058) at eloop.c:1228
error =
t =
ts = {tv_sec = 1, tv_nsec = 77999580}
tsp =
PRETTY_FUNCTION = "eloop_start"
#9 0x00000055868dda74 in main (argc=, argv=, envp=) at dhcpcd.c:2648
ctx = {pidfile = "/run/dhcpcd/port0.pid", '\000' <repeats 13 times>, vendor = "dhcpcd-10.2.2:Linux-6.1.130-manual-02457-g6b89e504bd2d:aarch64:AArch64", '\000' <repeats 185 times>, fork_fd = -1, cffile = 0x558af02340 "/etc/pnc-dhcpcd.conf", options = 310344232912607245, logfile = 0x0, argc = 5, argv = 0x7fe178a468, ifac = 0, ifav = 0x0, ifdc = 0, ifdv = 0x0, ifc = 1, ifv = 0x7fe178a488, ifcc = 1, ifcv = 0x558af175e0, duid_type = 0 '\000', duid = 0x558af23340 "", duid_len = 16, ifaces = 0x558af233a0, ctl_buf = 0x0, ctl_buflen = 0, ctl_bufpos = 0, ctl_extra = 0, routes = {rbt_root = 0x558af25118, rbt_ops = 0x55869314c0 <rt_compare_os_ops>, rbt_minmax = {0x558af05148, 0x558af25048}}, froutes = {rbt_root = 0x558af06a88, rbt_ops = 0x55869314e0 <rt_compare_free_ops>, rbt_minmax = {0x558af03608, 0x558af24f78}}, rt_order = 1, pf_inet_fd = 15, priv = 0x558af220d0, link_fd = 9, link_rcvbuf = 0, seq = 76, sseq = 0, sigset = {__val = {0 <repeats 16 times>}}, eloop = 0x558af17810, script = 0x558691b298 "/usr/libexec/dhcpcd-run-hooks", script_fp = 0x558af1b410, script_buf = 0x558af3a150 "PATH=/usr/bin:/usr/sbin:/bin:/sbin", script_buflen = 269, script_env = 0x558af04540, script_envlen = 49, control_fd = -1, control_unpriv_fd = -1, control_fds = {tqh_first = 0x558af22000, tqh_last = 0x558af22000}, control_sock = "/run/dhcpcd/port0.sock", '\000' <repeats 14 times>, control_sock_unpriv = "/run/dhcpcd/port0.unpriv.sock", '\000' <repeats 14 times>, control_group = 0, vivso = 0x0, vivso_len = 0, randomstate = 0x0, ps_user = 0x7fa8494668 , ps_processes = {tqh_first = 0x558af22ce0, tqh_last = 0x558af230e0}, ps_root = 0x558af22ce0, ps_inet = 0x558af22ec0, ps_ctl = 0x558af230e0, ps_data_fd = 8, ps_log_fd = -1, ps_log_root_fd = -1, ps_eloop = 0x558af22c40, ps_control = 0x558af22000, ps_control_client = 0x0, dhcp_opts = 0x558af13da0, dhcp_opts_len = 157, udp_rfd = -1, udp_wfd = -1, opt_buffer = 0x0, opt_buffer_len = 0, secret = 0x0, secret_len = 0, nd_fd = -1, ra_routers = 0x558af39730, nd_opts = 0x558af169d0, nd_opts_len = 7, dhcp6_rfd = -1, dhcp6_wfd = -1, dhcp6_opts = 0x558af1f940, dhcp6_opts_len = 84, dev_load = 0x0, dev_fd = -1, dev = 0x0, dev_handle = 0x0}
ifaddrs = 0x0
ifo = 0x0
ifp =
family = 0
opt =
oi = 4
i = 1
logopts =
t =
--Type for more, q to quit, c to continue without paging--
len =
pid =
fork_fd = {5, 6}
sig =
siga = 0x0
si = 1
func = "main"

(gdb) thread apply all bt

Thread 1 (LWP 17642):
#0 dhcp6_delegate_prefix (ifp=0x558af285e0) at dhcp6.c:3029
#1 dhcp6_bind (ifp=ifp@entry=0x558af285e0, op=op@entry=0x558691f960 "REPLY6", sfrom=sfrom@entry=0x7fe1779ac0 "fe80::5074:f2ff:feb1:a87f ") at dhcp6.c:3402
#2 0x000000558690e610 in dhcp6_recvif (len=, r=0x7fe1779cc0, sfrom=0x7fe1779ac0 "fe80::5074:f2ff:feb1:a87f ", ifp=) at dhcp6.c:3748
#3 dhcp6_recvmsg (ctx=, msg=, ia=ia@entry=0x0) at dhcp6.c:3886
#4 0x00000055869149b0 in ps_inet_dispatch (arg=, psm=, msg=) at privsep-inet.c:337
#5 0x00000055869118cc in ps_recvpsmsg (ctx=0x7fe1789e18, fd=, events=, callback=callback@entry=0x55869125b4 <ps_root_dispatchcb>, cbctx=0x7fe1789e18) at privsep.c:1181
#6 0x0000005586912434 in ps_root_dispatch (arg=, events=) at privsep-root.c:850
#7 0x00000055868e4b54 in eloop_run_ppoll (signals=0x7fe178a058, ts=, eloop=0x558af17810) at eloop.c:1106
#8 eloop_start (eloop=0x558af17810, signals=signals@entry=0x7fe178a058) at eloop.c:1228
#9 0x00000055868dda74 in main (argc=, argv=, envp=) at dhcpcd.c:2648

Fault seems to be in dhcp6_delegate_prefix() v10.2.2 dhcp6.c line 3029

state = D6_STATE(ifp);

/* Clear the logged flag. */
TAILQ_FOREACH(ap, &state->addrs, next) {
	ap->flags &= ~IPV6_AF_DELEGATEDLOG;
}

because state was during interface stop placed to null, what you can see from backtrace above.
I would like to add here patch:

state = D6_STATE(ifp);
if (state == NULL) {
	loginfox("%s: ignoring REPLY6, DHCP6 state is null", ifp->name);
	return;
}

/* Clear the logged flag. */
TAILQ_FOREACH(ap, &state->addrs, next) {
	ap->flags &= ~IPV6_AF_DELEGATEDLOG;
}

that would guard against NULL state.
This should ensure no crash in this case.