We tried changing children to 8 and the problem still occurs, 1 is the only safe value thus far.
Not sure exactly on the relationship between Kamailio and Libcrypto, does Kamailio need to interact with Libcrypto in a specific order? For example, if there are multiple messages sent to Kamailio both of which require some form of interaction with Libcrypto but one thread takes slightly than another, does it matter the order in which Kamailio interacts with Libcrypto?
Will look at installing debug symbols for libssl/libcrypto.