Odd tasmota/mqtt connection issue

I;'ve a mixture if zibgee and sonoff flashed with tasmota wifi devices and the last couple of days I’ve been getting issues with some of the tasmota devices not connecting to the mosquito MQTT broker.

network connection to the devices is solid, looking at the tasmota console output its a long stream of

17:04:25.285 MQT: Attempting connection...
17:04:25.498 MQT: Connect failed to 192.168.68.13:1883, rc -2. Retry in 120 sec
17:06:26.270 MQT: Attempting connection...
17:06:26.483 MQT: Connect failed to 192.168.68.13:1883, rc -2. Retry in 120 sec
17:08:27.267 MQT: Attempting connection...
17:08:27.480 MQT: Connect failed to 192.168.68.13:1883, rc -2. Retry in 120 sec

until suddenly, without me doing anything

17:54:50.279 MQT: Attempting connection...
17:54:50.491 MQT: Connect failed to 192.168.68.13:1883, rc -2. Retry in 120 sec
17:56:51.275 MQT: Attempting connection...
17:56:51.668 MQT: Connected
17:56:51.672 MQT: tele/tasmota_C8B84B/LWT = Online (retained)

its not happening to all the tasmota devices, just 2 seem to suffer with it. Restarting the device, MQTT broker, HA makes no difference

Any thoughts?

TFB