@dizzy_one 

What is the current network diagram? How do you connect these devices together? And what are their operation modes?

Try to connect one slave Deco to the main Deco only, with other Decos powered off, try to update the firmware of the slave Deco.

Meanwhile, you can try to reboot the Deco nodes and modem to give it a go; 

Besides, please ensure that the Deco app is up to date. 

Good day. 

@dizzy_one 

Thanks for your reply. 

Cause they have been updated to the latest firmware, you can keep an eye on it when the next firmware released. 

Meanwhile, we can use the web UI to update the firmware of the Deco; do not have to connect each Deco to the main modem to do that. 

Good day.