A late thanks for the extended infotorial! 
Imho the total number of devices below, are not real life numbers:
To me, these are real life numbers:
For Homey Pro 2019:
someone reported a very high number of 61 devices, but for most folks the zigbee net (performance & reliability) seems to go south when using more than 45 devices.
For Homey Pro 2023:
Emile (Athom) wrote 200 devices should be possible.
I did not see any posts of users actually using that number of zigbee devices.
On top of my head, one user reported using around 145 devices.
Interference
Zigbee, 2.4GHz wifi (called wifi from here) and Bluetooth use the same 2.4GHz band.
It’s very well possible your wifi and your neighbors’ wifi signals interfere with your zigbee signal.
Wifi has approx. 10 times more transmit power.
But, both systems use channels, for you to pick a channel on both wifi as well as zigbee.
Be aware of the fact the channels aren’t numbered the same.
Note: Homey has a ‘autotune’ function. When you set your wifi channel to preferably 1, 6 or 11, a zigbee reset will search for a quiet channel automatically.
Very useful info:
