Can Ubuntu "Sometimes" Fail to Generate Core Files? - c++

Question

I've configured an Amazon EC2 instance to generate core files when processes crash, and for the most part it works as expected. The problem is that it doesn't always work. The program that I have issues with is comprised of 9 concurrent processes working in concert via MPI. When this program crashes, I almost always get a core dump, but in some rare cases no core dump is generated, even though a segfault(11) was reported in my logs that are capturing stdErr. In other cases (very rare), the resulting core file is truncated.
I have not configured my core pattern, so only one core (named "core") can exist in the directory my process is launched from. Further details below my question.
How can no core dump be generated "sometimes"? Is it possible two processes are attempting to dump a core file at once, and both failing because they are in conflict? Are core dumps just not a reliable method of tracing bugs?
.bash_profile
export LD_LIBRARY_PATH=/usr/local/lib
source ./.bashrc
ulimit -c unlimited
/etc/security/limuits.conf
* soft core unlimited
root hard core unlimited
ulimit -a
core file size (blocks, -c) unlimited
data seg size (kbytes, -d) unlimited
scheduling priority (-e) 0
file size (blocks, -f) unlimited
pending signals (-i) 29879
max locked memory (kbytes, -l) 64
max memory size (kbytes, -m) unlimited
open files (-n) 1024
pipe size (512 bytes, -p) 8
POSIX message queues (bytes, -q) 819200
real-time priority (-r) 0
stack size (kbytes, -s) 8192
cpu time (seconds, -t) unlimited
max user processes (-u) 29879
virtual memory (kbytes, -v) unlimited
file locks (-x) unlimited
EDIT1
I've found a bug that will reliably omit a core file. In an attempt to generate a core when the program is in a suspicious state, I have inserted the following lines in several places:
if (value > FLT_MAX){
int *i=NULL;
*i=1;
}
About half of my processes reach one of these lines and segfault, probably within a few milliseconds of each other since they take almost identical code paths. I don't simply raise(SIGSEGV) because I've seen my program swallow that and continue before; perhaps because the signal technically doesn't require a quit?
EDIT2
Core files now include pid in their names:
sudo -s
echo "1" > /proc/sys/kernel/core_uses_pid
The issue still occurs. Are there restrictions in ubuntu that prevent it from writing more than one core file at a time in certain cases?