Zigbee2mqtt - devices drop off - weird behaviour

I have zigbee2mqtt running on an ubuntu server with a conbee II. After about 8 hours, half the network drops out and I lose half my devices.

Then the option for “Permit Join” is no longer available. All I have is Disable Join (ALL) in the drop down menu at the top, along with some of the devices still connected and the coordinator.

The map also takes forever to load.

I then turn everything off, come back the next day and everything is back to normal. The map is quick to load.

The conbee II is connected via 2m extension cable. My 2.4ghz WIFI is set to channel 12.

Can anyone advise what is going on?