CThere are many different factors that can add or remove lag from a system, whether it is zigbee or Z wave.
First, what is the brand and model of the switches? If these are the GE or Leviton that use an actual physical traveler wire between the auxiliary switch and the master, then the reason why you’re seeing no lag is because it’s not using the network at all. It’s just an electrical pulse from the auxiliary to the master over the traveler wire.
In a mesh network, whether it is zigbee or Z wave, each individual device keeps its own little neighbor table which shows the neighbors that are physically closest to it. This neighbor table is built at the time the device joined the network.
If, as many people do, you initially paired the device by bringing itclose to the hub and then you either move the device to its final location or you took the hub back to its usual location, that’s fine. That’s called “bench pairing.” But it means that the neighbor table will be incorrect, because it’s based on the neighbors at the time of the original pairing.
Another issue that can arise is if you add additional devices that are repeaters to your network. The new devices will have up-to-date neighbor tables. But the devices around them don’t even know that that new device exists. They are still working off of their old neighbor tables.
So how do you get the devices to update their neighbor tables? For Zigbee, it’s easy. Just take the hub off of power for at least 15 minutes. (Unplugged and remove any batteries from it.) You don’t have to do anything with the other devices. Eventually the other devices realize that the hub is missing, and they go into panic mode. Now when the hub comes back on power everybody will update their individual neighbor tables. It can take a little while for this to get done for every device, so you may not see any improvement until the next day, but this should improve the overall efficiency of your network.
( there’s a different procedure for zwave devices, with the same general idea.)
Whatever you add new devices to your network, or move devices from one physical location to another, you should do the procedure to get the neighbor tables updated.
This alone can greatly reduce the lag in a network.