Nextepc died in some MT-Fallback

Hello, In some situations the Nextepc is crashing when try the MT-CSFB. Here is the log: 07/17 17:48:53.270: [mme] WARNING: EMM_CAUSE : IMSI Unknown in HSS (mme-sm.c:339) 07/17 17:48:54.480: [mme] WARNING: ERROR DIAMETER Result Code(5001) (mme-fd-path.c:298) 07/17 17:48:54.480: [mme] WARNING: EMM_CAUSE : IMSI Unknown in HSS (mme-sm.c:339) 07/17 17:48:55.611: [s1ap] ERROR: Failed to encode S1AP-PDU[-1] (s1ap-encoder.c:41) 07/17 17:48:55.611: [mme] ERROR: s1ap_encode_pdu() failed (s1ap-build.c:555) 07/17 17:48:55.611: [mme] FATAL: s1ap_send_initial_context_setup_request: Assertion `rv == OGS_OK && s1apbuf' failed. (s1ap-path.c:252) File Logging: '//var/log/nextepc/mme.log' Configuration: '//etc/nextepc/mme.conf' 07/17 17:48:58.215: [mme] INFO: MME initialize...done (mme.c:28) NextEPC daemon v0.5.0.26-b642c 07/17 17:48:58.215: [gtp] INFO: gtp_server() [10.3.15.38]:2123 (gtp-path.c:36) 07/17 17:48:58.215: [gtp] INFO: gtp_server() [2804:828:3:15:b010:37ff:fe46:4521]:2123 (gtp-path.c:36) 07/17 17:48:58.215: [gtp] INFO: gtp_server() [2804:828:3:208:48a0:1cff:fed9:b7c9]:2123 (gtp-path.c:36) 07/17 17:48:58.215: [gtp] INFO: gtp_connect() [127.0.0.2]:2123 (gtp-path.c:61) 07/17 17:48:58.216: [mme] INFO: sgsap client() [127.0.0.1]:29118 (sgsap-lkpath.c:47) 07/17 17:48:58.216: [mme] INFO: s1ap_server() [10.3.15.38]:36412 (s1ap-lkpath.c:44) 07/17 17:48:58.217: [fd] INFO: CONNECTED TO 'hss.localdomain' (TCP,soc#14): (fd-logger.c:113) 07/17 17:48:58.802: [mme] INFO: eNB-S1 accepted[10.12.0.3]:36412 in s1_path module (s1ap-lkpath.c:70) In the attached file is the pcap from this moment, I will try to find what is happened. Thanks Romeu Medeiros