Signer segfaulting after SoftHSM access and pthreading problems

No functional problems with OpenDNSSEC, but after a few days the signer starts having problems with access to the SoftHSM file, followed by pthread problems, until ods-signerd crashes with a segfault:

Sep 1 21:09:35 services ods-signerd: SoftHSM: init: Could not open token database. Probably wrong privileges: /var/softhsm/
slot0.db
Sep 1 21:09:35 services ods-signerd: [hsm] idle libhsm connection, trying to reopen
Sep 1 21:09:35 services ods-signerd: [hsm] libhsm connection opened succesfully
Sep 1 21:09:35 services ods-signerd: [hsm] error signing rrset with libhsm
Sep 1 21:09:35 services ods-signerd: [rrset] unable to sign RRset[6]: lhsm_sign() failed
Sep 1 21:09:35 services ods-signerd: [hsm] error signing rrset with libhsm
Sep 1 21:09:35 services ods-signerd: [rrset] unable to sign RRset[50]: lhsm_sign() failed
Sep 1 21:09:35 services ods-signerd: [hsm] error signing rrset with libhsm
Sep 1 21:09:35 services ods-signerd: [worker[2]] sign zone chiplist.com failed: 2 RRsets failed
Sep 1 21:09:35 services ods-signerd: [rrset] unable to sign RRset[6]: lhsm_sign() failed
Sep 1 21:09:35 services ods-signerd: [worker[2]] CRITICAL: failed to sign zone chiplist.com: General error
Sep 1 21:09:35 services ods-signerd: [worker[2]] backoff task [sign] for zone chiplist.com with 60 seconds
Sep 1 21:09:35 services ods-signerd: [hsm] error signing rrset with libhsm
Sep 1 21:09:35 services ods-signerd: [rrset] unable to sign RRset[28]: lhsm_sign() failed
Sep 1 21:09:35 services ods-signerd: [worker[3]] sign zone processor-portal.com failed: 2 RRsets failed
Sep 1 21:09:35 services ods-signerd: [worker[3]] CRITICAL: failed to sign zone processor-portal.com: General error
Sep 1 21:09:35 services ods-signerd: [worker[3]] backoff task [sign] for zone processor-portal.com with 60 seconds
...
Sep 1 21:10:02 services ods-signerd: SoftHSM: init: Could not open token database. Probably wrong privileges: /var/softhsm/slot0.db
Sep 1 21:10:02 services ods-signerd: [hsm] idle libhsm connection, trying to reopen
Sep 1 21:10:02 services ods-signerd: daemon/engine.c at 442 could not pthread_join(engine->drudgers[i]->thread_id, NULL): Invalid argument
Sep 1 21:10:04 services ods-signerd: daemon/engine.c at 442 could not pthread_join(engine->drudgers[i]->thread_id, NULL): Invalid argument
Sep 1 21:10:04 services ods-signerd: daemon/engine.c at 442 could not pthread_join(engine->drudgers[i]->thread_id, NULL): No such process
Sep 1 21:10:04 services ods-signerd: daemon/engine.c at 442 could not pthread_join(engine->drudgers[i]->thread_id, NULL): No such process
Sep 1 21:10:04 services ods-signerd: [hsm] libhsm connection opened succesfully
Sep 1 21:10:05 services ods-signerd: [hsm] error signing rrset with libhsm
Sep 1 21:10:05 services ods-signerd: [rrset] unable to sign RRset[6]: lhsm_sign() failed
Sep 1 21:10:05 services ods-signerd: [worker[3]] sign zone techamatic.net failed: 1 RRsets failed
Sep 1 21:10:05 services ods-signerd: [worker[3]] CRITICAL: failed to sign zone techamatic.net: General error
...
Sep 3 15:59:03 services ods-signerd: SoftHSM: init: Could not open token database. Probably wrong privileges: /var/softhsm/slot0.db
Sep 3 15:59:03 services ods-signerd: [hsm] idle libhsm connection, trying to reopen
Sep 3 15:59:04 services ods-signerd: SoftHSM: init: Could not open token database. Probably wrong privileges: /var/softhsm/slot0.db
Sep 3 15:59:04 services ods-signerd: [zone] unable to prepare signing keys for zone processor-portal.org: error creating libhsm context
Sep 3 15:59:04 services ods-signerd: [worker[1]] CRITICAL: failed to sign zone processor-portal.org: HSM error
Sep 3 15:59:04 services ods-signerd: [worker[1]] backoff task [sign] for zone processor-portal.org with 60 seconds
Sep 3 15:59:05 services ods-signerd: SoftHSM: OSDestroyMutex: Failed to destroy POSIX mutex
Sep 3 15:59:06 services kernel: ods-signerd[17589]: segfault at 25 ip 0000000000000025 sp 00007ff072da99d8 error 4
...
ep 4 14:53:41 services ods-signerd: SoftHSM: init: Could not open token database. Probably wrong privileges: /var/softhsm/slot0.db
Sep 4 14:53:41 services ods-signerd: [hsm] idle libhsm connection, trying to reopen
Sep 4 14:53:41 services ods-signerd: daemon/engine.c at 442 could not pthread_join(engine->drudgers[i]->thread_id, NULL): Invalid argument
Sep 4 14:53:43 services ods-signerd: [hsm] idle libhsm connection, trying to reopen
Sep 4 14:53:43 services ods-signerd: daemon/engine.c at 442 could not pthread_join(engine->drudgers[i]->thread_id, NULL): Invalid argument
Sep 4 14:53:43 services ods-signerd: daemon/engine.c at 442 could not pthread_join(engine->drudgers[i]->thread_id, NULL): Invalid argument
...
Sep 4 14:53:44 services ods-signerd: SoftHSM: init: Could not open token database. Probably wrong privileges: /var/softhsm/slot0.db
Sep 4 14:53:44 services ods-signerd: [hsm] idle libhsm connection, trying to reopen
Sep 4 14:53:44 services ods-signerd: daemon/engine.c at 442 could not pthread_join(engine->drudgers[i]->thread_id, NULL): Invalid argument
Sep 4 14:53:44 services ods-signerd: daemon/engine.c at 442 could not pthread_join(engine->drudgers[i]->thread_id, NULL): Invalid argument
Sep 4 14:53:44 services ods-signerd: daemon/engine.c at 442 could not pthread_join(engine->drudgers[i]->thread_id, NULL): Invalid argument
Sep 4 14:53:44 services ods-signerd: daemon/engine.c at 442 could not pthread_join(engine->drudgers[i]->thread_id, NULL): Invalid argument
Sep 4 14:53:44 services ods-signerd: daemon/engine.c at 442 could not pthread_join(engine->drudgers[i]->thread_id, NULL): Invalid argument
Sep 4 14:53:44 services ods-signerd: daemon/engine.c at 442 could not pthread_join(engine->drudgers[i]->thread_id, NULL): Invalid argument
Sep 4 14:53:44 services kernel: ods-signerd[5052]: segfault at 7f4f035fe9d0 ip 00007f4f0cd0d143 sp 00007f4f0939ace0 error 4 in libpthread-2.12.so[7f4f0cd05000+17000]

The token file /var/softhsm/slot0.db has permissions 640 root:ods
and both the Signer and Enforcer run as ods:ods.