I can't reproduce this:
0(15468) DEBUG: <core> [core/udp_server.c:491]: udp_rcv_loop(): received on udp socket: (90/87/87) [[REGISTER sip:1.2.3.4:5060 SIP/2.0 0A Via: SIP/2.0/UDP 1.2.3.4:5060;branch=z9hG4bK724588683]] 0(15468) DEBUG: <core> [core/parser/msg_parser.c:610]: parse_msg(): SIP Request: 0(15468) DEBUG: <core> [core/parser/msg_parser.c:612]: parse_msg(): method: <REGISTER> 0(15468) DEBUG: <core> [core/parser/msg_parser.c:614]: parse_msg(): uri: sip:1.2.3.4:5060 0(15468) DEBUG: <core> [core/parser/msg_parser.c:616]: parse_msg(): version: <SIP/2.0> 0(15468) ERROR: <core> [core/parser/parse_via.c:1324]: parse_via_param(): failure parsing via param 0(15468) ERROR: <core> [core/parser/parse_via.c:2704]: parse_via(): parsing via on: <SIP/2.0/UDP 1.2.3.4:5060;branch=z9hG4bK724588683> 0(15468) ERROR: <core> [core/parser/parse_via.c:2710]: parse_via(): via parse error 0(15468) ERROR: <core> [core/parser/msg_parser.c:125]: get_hdr_field(): bad via 0(15468) DEBUG: <core> [core/parser/msg_parser.c:279]: get_hdr_field(): error exit 0(15468) ERROR: <core> [core/parser/msg_parser.c:337]: parse_headers(): bad header field [Via: SIP/2.0/UDP 1.2.3.4:5060;branch=z9hG4bK724588683] 0(15468) ERROR: <core> [core/parser/msg_parser.c:681]: parse_msg(): ERROR: parse_msg: message=<REGISTER sip:1.2.3.4:5060 SIP/2.0 Via: SIP/2.0/UDP 1.2.3.4:5060;branch=z9hG4bK724588683> 0(15468) ERROR: <core> [core/receive.c:231]: receive_msg(): core parsing of SIP message failed (127.0.0.1:38418/1)
./kamailio -V version: kamailio 5.2.0-dev7 (x86_64/linux) 491e19
Can you post a backtrace with gdb, and ideally a debug log of the crash?