Hi there.
I have 8 GU10 spots in my house.
3 of them is stuck at firmware updating - the rest is OK and is updated to latest firmware version.
They have been stuck for about 4 weeks, but is working with the rest of the lights.
I can’t find a way to cancel the update - I have tried restarting Z2M and remove the power from the spots - no joy.
I’m running the latest version of HA and Zigbee2MQTT
Thanks in advance
I have had that too.
The update has happened, but the status has not changed.
It turns out the status is from the bulbs, so you need to cut the power on the bulbs and wait a few minutes before reconnecting it.
Cool - I will try that!
Did it fix it for you? I have tried this but no luck for me 
Still showing ‘Installing’
Okay, this needs to be clarified for others that come here.
Zigbee is a low bandwidth protocol and updates are being transmitted with the lowest possible priority to not hinder the normal work processes in the network.
This means updates can take hours and maybe even a few days to propagate through the network, so have patience! Lots of patience!.
The OP here had the status for several weeks and that was why I recommended the reboot of the bulbs.