MQTT Client Disconnecting Every Minute - UDP Sync? (GIT8266O-409)

[pirlite2]

Using the latest pulled version.

I have an MQTT client working fine adapted from an example program; I can subscribe and publish even at QoS2. Except the client disconnects around every minute (e.g. 134 disconnections/reconnections in a timed 137 minute period). The log output for a cycle between connections is shown below (the "MQTT connected" and "MQTT subscribed" messages are mine):

...
MQTT connected
D (8783553) MQTT_CLIENT: msg_type=5, msg_id=8349
D (8783559) MQTT_CLIENT: received MQTT_MSG_TYPE_PUBREC
D (8783571) MQTT_CLIENT: msg_type=9, msg_id=45734
D (8783575) MQTT_CLIENT: pending_id=45734, pending_msg_count = 2
D (8783582) MQTT_CLIENT: Subscribe successful
MQTT subscribed
D (8783591) MQTT_CLIENT: msg_type=7, msg_id=8349
D (8783597) MQTT_CLIENT: received MQTT_MSG_TYPE_PUBCOMP
D (8783605) MQTT_CLIENT: pending_id=45734, pending_msg_count = 1
D (8783614) OUTBOX: DELETED msgid=8349, msg_type=3, remain size=0
D (8783623) MQTT_CLIENT: Receive MQTT_MSG_TYPE_PUBCOMP, finish QoS2 publish
MQTT published
D (8813650) MQTT_CLIENT: Sent PING successful
D (8813655) MQTT_CLIENT: PING sent
D (8813658) MQTT_CLIENT: msg_type=13, msg_id=0
D (8813662) MQTT_CLIENT: MQTT_MSG_TYPE_PINGRESP
D (8828435) udp_sync: UDP sync cache udp 0x40108048
D (8828441) udp_sync: UDP sync clear udp 0x40108048
D (8828447) udp_sync: UDP sync cache udp 0x40108048
D (8828452) udp_sync: UDP sync clear udp 0x40108048
D (8828457) udp_sync: UDP sync cache udp 0x40108048
D (8828462) udp_sync: UDP sync clear udp 0x40108048
D (8828468) udp_sync: UDP sync cache udp 0x40108048
D (8828473) udp_sync: UDP sync clear udp 0x40108048
E (8828481) TRANS_TCP: tcp_poll_read select error 113, errno = Software caused connection abort, fd = 0
E (8828495) MQTT_CLIENT: Read error or end of stream
I (8828504) MQTT_CLIENT: Reconnect after 10000 ms
MQTT disconnected
D (8838511) MQTT_CLIENT: Reconnecting...
D (8843514) TRANS_TCP: [sock=0],connecting to server IP:172.16.0.1,Port:1883...
D (8843530) MQTT_CLIENT: Transport connected to mqtt://172.16.0.1:1883
I (8843536) MQTT_CLIENT: Sending MQTT CONNECT message, type: 1, id: 0000
D (8843552) MQTT_CLIENT: Connected
D (8843555) MQTT_CLIENT: mqtt_enqueue id: 0, type=1 successful
D (8843561) MQTT_CLIENT: mqtt_enqueue id: 46230, type=3 successful
D (8843568) OUTBOX: ENQUEUE msgid=46230, msg_type=3, len=46, size=46
D (8843575) MQTT_CLIENT: Sent subscribe topic=trv, id: 26140, type=8 successful
I (8843585) simple wifi: sent subscribe successfully to trv
MQTT connected
...

The actual disconnect seems to occur with:

TRANS_TCP: tcp_poll_read select error 113, errno = Software caused connection abort, fd = 0

which I am interpreting as a socket error; the fd (file descriptor?) value of zero looks suspicious.

Now it may be coincidence, but every disconnect seems to be preceded by a series of udp_sync messages, which puzzles me as I cannot see where I am using UDP. In fact, investigating the the udp_sync_cache and udp_sync_clear functions, I can see an if-statement that skips the udp-sync operation if the sys_current_task_is_tcpip function returns true, which would seem reasonable, but is not happening. I cannot find the sys_current_task_is_tcpip function.

The reconnections all require a single attempt apart from the second which always needs 9 reconnection attempts - puzzling.

Any suggestions/guidance oh this? In particular, the UDP sync stuff looks very odd.

Peter