Serious range issue with Nous A1Z smart plugs

Hello All,
I just bought a few A1Z smart plugs from Nous. Coupling works quick and easy, as long as I stay within 1m of my Homey Pro and they switch on and off correctly. Unfortunately, all three devices don’t switch reliably at a line-of-sight distance of 2m and don’t work at 5m anymore (just air, no walls). Are the devices faulty? Does anyone have any experience with those plugs?
THX, Michael

Max 3 to 5 meters is quite a normal signal range indoors.
But you probably don’t know they can extend the zigbee network?
https://support.homey.app/hc/en-us/articles/10374465562652-Creating-a-stable-Zigbee-network-with-Homey-Pro-Early-2023

Often interference shortens the usable range, or even cripples a zigbee mesh network.
Wifi 2.4GHz can interfere badly (including close neighbour’s wifi signals)
Make sure to set the channel to preferably 1, 6 or 11 and set the zigbee channel to a non- or low interfering one

Extended hints and tricks:

I do have a lot of this devices and on many places also after a range extender in the gardenhouse.

No problems at all. Reliable, stable and useful.

Are they running the latest firmware? Perhaps that could maybe improve, but not sure about that, because on the previous firmware I did not find any trouble as well