Athom recommends using no more than 30-40 Zigbee devices (source). However, there are users who have no problems even with 60 ZigBee devices. I myself have 36 ZigBee devices and no problems.
The most important points with ZigBee are:
– check if ZigBee and WiFi channel do not interfere with each other (link)
– first connect the powered devices, ideally 15 of them
– use enough powered devices, because they work as repeaters and forward signals (mesh)
With Z-Wave is it near the same. Enough repeaters are needed to create a stable network/mesh. However, it is not absolutely necessary to pair the powered devices first, but it is definitely recommended. The maximum number of devices is 231 (source).
I have specified my statement a little more precisely. I hope at least.
But what I actually meant was that if you use enough wall plugs, light switches, lamps, there is actually no need to use repeaters/range extender without function, such as this one from Aeotec:
It’s not possible to give a general answer to this question. I myself have 4 battery-powered devices of the maximum 15 direct connection points to Homey, and I have no problems.
How many battery-powered devices have you connected within the first 15 IDs?
The problem is that a maximum of approx. only 15 devices can be connected directly to Homey. Other devices are then connected to Homey via routers. And if you now already have many battery-powered devices among the first 15 devices, then only a few repeaters can be connected to Homey. The number of devices that can be connected via a repeater with Homey is also limited.
Maybe @Dijker knows the maximum number? I don’t.