I've ran into issue where MongoDB connection from PHP works correctly, if only one host is specified in the connection string. However, trying to use replicaSet results in PHP process being aborted.

#0 0x00007f2f161b42c7 in raise () from /lib64/libc.so.6
#1 0x00007f2f161b59b8 in abort () from /lib64/libc.so.6
#2 0x00007f2f161f6e17 in __libc_message () from /lib64/libc.so.6
#3 0x00007f2f16295b67 in __fortify_fail () from /lib64/libc.so.6
#4 0x00007f2f16295b22 in __stack_chk_fail () from /lib64/libc.so.6
#5 0x00007f2efe76400a in mongoc_stream_tls_openssl_new (
base_stream=base_stream@entry=0x55a498722700,
host=0x55a498230c98 "2a01:4f8:173:1828::40", opt=0x55a498231968,
client=<optimized out>)
at /usr/src/debug/php-pecl-mongodb-1.6.0~alpha2/NTS/src/libmongoc/src/libmongoc/src/mongoc/mongoc-stream-tls-openssl.c:777
#6 0x00007f2efe762854 in mongoc_stream_tls_new_with_hostname (
base_stream=base_stream@entry=0x55a498722700, host=<optimized out>,
opt=<optimized out>, client=client@entry=1)

(...)

I am able to reproduce the problem both with 1.6.0alpha2 and 1.5.5.

Please take a look at the attached mongo debug log, and gdb backtrace.