Zigbee2mqtt grouping not working

Hi,
I recently discovered z2m grouping for my lights.
Until now, I was grouping my lights from HA UI, but it appeared that my coordinator (conbee 2) was not able to send all the messages individually to all my devices (25+).

I then started to group devices through zigbee2mqtt directly, which would theoretically allow me to send a on / off command to the newly created entity in HA once.

The thing is that I have a very strange behavior…

When I switch the lights on and off, through HA, the order appears to be sent and zigbee2mqtt and HA display a new state for all the entities in the group.

IE : I switch the lights group to ON, all the lights appear to be ON in HA AND Z2M.

The problem is that they DON’T actually switch on and off : they remain in their previous state.

The only thing I can do is to individually put my lights in their correct states so I can switch them on and off again…

To be very accurate, this does not appear to be a problem of switch numbers : whatever is the number of devices in the group (3 or 25), the problem remains.

This behavior is very strange, what’s your point of view ?

Thanks in advance.