Denis Butin wrote in an email:

I had crashes with Ubuntu 16.10, which uses GCC 6 instead of GCC 5. There may be a link with the aforementioned warnings. Taking a closer look with gdb showed a segfault that went away once I commented out the following lines:

In s3_clnt.c:
OQS_KEX_free(oqskex_kex);
OQS_RAND_free(oqskex_rand);

In s3_srvr.c:
OQS_KEX_free(s->s3->tmp.oqskex_kex);
OQS_RAND_free(s->s3->tmp.oqskex_rand);