I have a process stuck in a stopped state (I do not know why it was stopped). Process information in the kernel can be changed ('procstat -i' below shows that SIGTERM and SIGKILL were sent), but it is unkillable and does not respond to SIGCONT.
Both gdb and truss simply wait after attaching to the process. I am keeping this system up for a while, so I can gather more information if needed.

Info:

# uname -a
FreeBSD candace.robotsondrugs.com 10.1-STABLE FreeBSD 10.1-STABLE #0 r283319: Sat May 23 14:41:09 CDT 2015     root@candace.robotsondrugs.com:/usr/obj/usr/src/sys/GENERIC  amd64

# uname -UK
1001515 1001515

# procstat -k 86319
  PID    TID COMM             TDNAME           KSTACK
86319 100485 transmission-daemon transmission-dae mi_switch sleepq_timedwait_sig _sleep kern_kevent sys_kevent amd64_syscall Xfast_syscall
86319 100910 transmission-daemon transmission-dae mi_switch thread_suspend_switch thread_single exit1 sys_sys_exit amd64_syscall Xfast_syscall

# procstat -i 86319
  PID COMM             SIG     FLAGS
86319 transmission-daemon HUP      --C
86319 transmission-daemon INT      P-C
86319 transmission-daemon QUIT     ---
86319 transmission-daemon ILL      ---
86319 transmission-daemon TRAP     ---
86319 transmission-daemon ABRT     ---
86319 transmission-daemon EMT      ---
86319 transmission-daemon FPE      ---
86319 transmission-daemon KILL     P--
86319 transmission-daemon BUS      ---
86319 transmission-daemon SEGV     ---
86319 transmission-daemon SYS      ---
86319 transmission-daemon PIPE     -I-
86319 transmission-daemon ALRM     ---
86319 transmission-daemon TERM     P-C
86319 transmission-daemon URG      -I-
86319 transmission-daemon STOP     P--
86319 transmission-daemon TSTP     ---
86319 transmission-daemon CONT     ---
86319 transmission-daemon CHLD     -I-
86319 transmission-daemon TTIN     ---
86319 transmission-daemon TTOU     ---
86319 transmission-daemon IO       -I-
86319 transmission-daemon XCPU     ---
86319 transmission-daemon XFSZ     ---
86319 transmission-daemon VTALRM   ---
86319 transmission-daemon PROF     ---
86319 transmission-daemon WINCH    -I-
86319 transmission-daemon INFO     -I-
86319 transmission-daemon USR1     ---
86319 transmission-daemon USR2     ---
86319 transmission-daemon 32       --C
... (all other signals have no flags)

# ps lax | grep trans
1001 86319     1   0  20   0 1011412 106776 -        Ts    -    1832:44.72 /usr/local/bin/transmission-daemon -g /usr/local/etc/transmission/home -w /mnt/storage/transmission -x /var/run/transmission/daemon.pid


It filled up a listen queue for a while before becoming completely unresponsive:
# netstat -Lan
Current listen queue sizes (qlen/incqlen/maxqlen)
Proto Listen         Local Address
...
tcp6  0/0/128        *.51413
tcp4  193/0/128      *.51413
tcp4  3/0/128        *.9091
...