There is one strange moment that I forgot to mention above, in the logs exactly at the moment when the service began to refuse, the recording disappears completely for 7 minutes, absolutely no entries, after which the recording of the TSP queue overflow begins.
Oct 3 18:38:07 sip1-life3 kamailio[3380553]: CRITICAL: {2 3691 INVITE 672699d1-c76b-4153-b72a-fe647913a9e9} tm [../../core/forward.h:292]: msg_send_buffer(): tcp_send failed Oct 3 18:38:09 sip1-life3 kamailio[3380539]: CRITICAL: {2 3691 INVITE 672699d1-c76b-4153-b72a-fe647913a9e9} tm [../../core/forward.h:292]: msg_send_buffer(): tcp_send failed Oct 3 18:38:12 sip1-life3 kamailio[3380534]: CRITICAL: {2 30106 INVITE 032f8650-1d90-49ed-82f1-c50ccbef191d} tm [../../core/forward.h:292]: msg_send_buffer(): tcp_send failed Oct 3 18:45:14 sip1-life3 /usr/local/sbin/kamailio[3380778]: CRITICAL: <core> [core/tcp_main.c:4170]: send2child(): tcp child 11, socket 224: queue full, 285 requests queued (total handled 2899418) Oct 3 18:45:15 sip1-life3 /usr/local/sbin/kamailio[3380778]: CRITICAL: <core> [core/tcp_main.c:4170]: send2child(): tcp child 1, socket 204: queue full, 286 requests queued (total handled 2964063) Oct 3 18:45:15 sip1-life3 /usr/local/sbin/kamailio[3380778]: CRITICAL: <core> [core/tcp_main.c:4170]: send2child(): tcp child 4, socket 210: queue full, 286 requests queued (total handled 2923484) Oct 3 18:45:15 sip1-life3 /usr/local/sbin/kamailio[3380778]: CRITICAL: <core> [core/tcp_main.c:4170]: send2child(): tcp child 6, socket 214: queue full, 286 requests queued (total handled 2911633) Oct 3 18:45:15 sip1-life3 /usr/local/sbin/kamailio[3380778]: CRITICAL: <core> [core/tcp_main.c:4170]: send2child(): tcp child 7, socket 216: queue full, 286 requests queued (total handled 2907132) Oct 3 18:45:15 sip1-life3 /usr/local/sbin/kamailio[3380778]: CRITICAL: <core> [core/tcp_main.c:4170]: send2child(): tcp child 8, socket 218: queue full, 286 requests queued (total handled 2903281) Oct 3 18:45:15 sip1-life3 /usr/local/sbin/kamailio[3380778]: CRITICAL: <core> [core/tcp_main.c:4170]: send2child(): tcp child 9, socket 220: queue full, 286 requests queued (total handled 2903438) Oct 3 18:45:15 sip1-life3 /usr/local/sbin/kamailio[3380778]: CRITICAL: <core> [core/tcp_main.c:4170]: send2child(): tcp child 11, socket 224: queue full, 286 requests queued (total handled 2899419) Oct 3 18:45:15 sip1-life3 /usr/local/sbin/kamailio[3380778]: CRITICAL: <core> [core/tcp_main.c:4170]: send2child(): tcp child 12, socket 226: queue full, 286 requests queued (total handled 2897842) Oct 3 18:45:16 sip1-life3 /usr/local/sbin/kamailio[3380778]: CRITICAL: <core> [core/tcp_main.c:4170]: send2child(): tcp child 16, socket 234: queue full, 286 requests queued (total handled 2895429) Oct 3 18:45:16 sip1-life3 /usr/local/sbin/kamailio[3380778]: CRITICAL: <core> [core/tcp_main.c:4170]: send2child(): tcp child 17, socket 236: queue full, 286 requests queued (total handled 2895303) Oct 3 18:45:16 sip1-life3 /usr/local/sbin/kamailio[3380778]: CRITICAL: <core> [core/tcp_main.c:4170]: send2child(): tcp child 22, socket 246: queue full, 286 requests queued (total handled 2891873) Oct 3 18:45:16 sip1-life3 /usr/local/sbin/kamailio[3380778]: CRITICAL: <core> [core/tcp_main.c:4170]: send2child(): tcp child 26, socket 254: queue full, 286 requests queued (total handled 2892619) Oct 3 18:45:16 sip1-life3 /usr/local/sbin/kamailio[3380778]: CRITICAL: <core> [core/tcp_main.c:4170]: send2child(): tcp child 27, socket 256: queue full, 286 requests queued (total handled 2891769) Oct 3 18:45:16 sip1-life3 /usr/local/sbin/kamailio[3380778]: ERROR: <core> [core/tcp_main.c:3458]: send_fd_queue_run(): send_fd failed on socket 224 , queue entry 0, retries 98, connection 0x7f0b6d974348, tcp so Oct 3 18:45:16 sip1-life3 /usr/local/sbin/kamailio[3380778]: CRITICAL: <core> [core/tcp_main.c:4170]: send2child(): tcp child 30, socket 262: queue full, 286 requests queued (total handled 2891614) Oct 3 18:45:16 sip1-life3 /usr/local/sbin/kamailio[3380778]: CRITICAL: <core> [core/tcp_main.c:4170]: send2child(): tcp child 31, socket 264: queue full, 286 requests queued (total handled 2890778) Oct 3 18:45:16 sip1-life3 /usr/local/sbin/kamailio[3380778]: CRITICAL: <core> [core/tcp_main.c:4170]: send2child(): tcp child 33, socket 268: queue full, 286 requests queued (total handled 2890852) Oct 3 18:45:16 sip1-life3 /usr/local/sbin/kamailio[3380778]: CRITICAL: <core> [core/tcp_main.c:4170]: send2child(): tcp child 0, socket 202: queue full, 287 requests queued (total handled 3071438) Oct 3 18:45:17 sip1-life3 /usr/local/sbin/kamailio[3380778]: CRITICAL: <core> [core/tcp_main.c:4170]: send2child(): tcp child 1, socket 204: queue full, 287 requests queued (total handled 2964064) Oct 3 18:45:17 sip1-life3 /usr/local/sbin/kamailio[3380778]: CRITICAL: <core> [core/tcp_main.c:4170]: send2child(): tcp child 2, socket 206: queue full, 287 requests queued (total handled 2944928) Oct 3 18:45:17 sip1-life3 /usr/local/sbin/kamailio[3380778]: CRITICAL: <core> [core/tcp_main.c:4170]: send2child(): tcp child 4, socket 210: queue full, 287 requests queued (total handled 2923485) Oct 3 18:45:17 sip1-life3 /usr/local/sbin/kamailio[3380778]: CRITICAL: <core> [core/tcp_main.c:4170]: send2child(): tcp child 5, socket 212: queue full, 287 requests queued (total handled 2915778) Oct 3 18:45:17 sip1-life3 /usr/local/sbin/kamailio[3380778]: CRITICAL: <core> [core/tcp_main.c:4170]: send2child(): tcp child 6, socket 214: queue full, 287 requests queued (total handled 2911634) Oct 3 18:45:17 sip1-life3 /usr/local/sbin/kamailio[3380778]: CRITICAL: <core> [core/tcp_main.c:4170]: send2child(): tcp child 7, socket 216: queue full, 287 requests queued (total handled 2907133) Oct 3 18:45:17 sip1-life3 /usr/local/sbin/kamailio[3380778]: CRITICAL: <core> [core/tcp_main.c:4170]: send2child(): tcp child 8, socket 218: queue full, 287 requests queued (total handled 2903282) Oct 3 18:45:17 sip1-life3 /usr/local/sbin/kamailio[3380778]: CRITICAL: <core> [core/tcp_main.c:4170]: send2child(): tcp child 9, socket 220: queue full, 287 requests queued (total handled 2903439) Oct 3 18:45:17 sip1-life3 /usr/local/sbin/kamailio[3380778]: CRITICAL: <core> [core/tcp_main.c:4170]: send2child(): tcp child 10, socket 222: queue full, 287 requests queued (total handled 2900227) Oct 3 18:45:17 sip1-life3 /usr/local/sbin/kamailio[3380778]: CRITICAL: <core> [core/tcp_main.c:4170]: send2child(): tcp child 11, socket 224: queue full, 287 requests queued (total handled 2899420) Oct 3 18:45:17 sip1-life3 /usr/local/sbin/kamailio[3380778]: CRITICAL: <core> [core/tcp_main.c:4170]: send2child(): tcp child 12, socket 226: queue full, 287 requests queued (total handled 2897843) Oct 3 18:45:17 sip1-life3 /usr/local/sbin/kamailio[3380778]: ERROR: <core> [core/tcp_main.c:3458]: send_fd_queue_run(): send_fd failed on socket 204 , queue entry 0, retries 88, connection 0x7f0b742a1968, tcp so Oct 3 18:45:17 sip1-life3 /usr/local/sbin/kamailio[3380778]: CRITICAL: <core> [core/tcp_main.c:4170]: send2child(): tcp child 13, socket 228: queue full, 287 requests queued (total handled 2896210) Oct 3 18:45:17 sip1-life3 /usr/local/sbin/kamailio[3380778]: ERROR: <core> [core/tcp_main.c:3458]: send_fd_queue_run(): send_fd failed on socket 210 , queue entry 0, retries 86, connection 0x7f0b74ffaa08, tcp so Oct 3 18:45:17 sip1-life3 /usr/local/sbin/kamailio[3380778]: CRITICAL: <core> [core/tcp_main.c:4170]: send2child(): tcp child 16, socket 234: queue full, 287 requests queued (total handled 2895430) Oct 3 18:45:17 sip1-life3 /usr/local/sbin/kamailio[3380778]: ERROR: <core> [core/tcp_main.c:3458]: send_fd_queue_run(): send_fd failed on socket 214 , queue entry 0, retries 88, connection 0x7f0b75003218, tcp so Oct 3 18:45:17 sip1-life3 /usr/local/sbin/kamailio[3380778]: ERROR: <core> [core/tcp_main.c:3458]: send_fd_queue_run(): send_fd failed on socket 216 , queue entry 1, retries 86, connection 0x7f0b75007620, tcp so Oct 3 18:45:17 sip1-life3 /usr/local/sbin/kamailio[3380778]: ERROR: <core> [core/tcp_main.c:3458]: send_fd_queue_run(): send_fd failed on socket 218 , queue entry 2, retries 84, connection 0x7f0b74772f70, tcp so Oct 3 18:45:17 sip1-life3 /usr/local/sbin/kamailio[3380778]: CRITICAL: <core> [core/tcp_main.c:4170]: send2child(): tcp child 17, socket 236: queue full, 287 requests queued (total handled 2895304) Oct 3 18:45:17 sip1-life3 /usr/local/sbin/kamailio[3380778]: ERROR: <core> [core/tcp_main.c:3458]: send_fd_queue_run(): send_fd failed on socket 220 , queue entry 0, retries 87, connection 0x7f0b74777378, tcp so Oct 3 18:45:17 sip1-life3 /usr/local/sbin/kamailio[3380778]: ERROR: <core> [core/tcp_main.c:3458]: send_fd_queue_run(): send_fd failed on socket 224 , queue entry 1, retries 83, connection 0x7f0b7477fb88, tcp so Oct 3 18:45:17 sip1-life3 /usr/local/sbin/kamailio[3380778]: CRITICAL: <core> [core/tcp_main.c:4170]: send2child(): tcp child 21, socket 244: queue full, 287 requests queued (total handled 2893042)