A correlation between the Wi-Fi network and the poor performance of Z-Wave network is not causation. Based on the details provided above, as others indicated, the symptoms are those of an overloaded mesh. As @bcopeland pointed out earlier, the problems may be related to the drivers.
Our engineers have tested different versions of the models you own, so there is highly likely that they run different firmware versions than those that we have tested.
In the ideal world, a manufacturer wouldn't produce different versions of the same basic model, but more often than not, big companies like Fibaro are known to release variations of the same model that are different enough to cause problems - another company that comes to mind is Schlage.
Using models that have been tested by our engineers, is the best way to avoid any issues. Sending us devices so that our engineers can test and adjust drivers based on the firmware variation, is another way.
Of course if enough customers report problems with a specific model that is running a different firmware, then our engineers run out and purchase the specific model so they can adjust the driver (or remove the model altogether from the List of Compatible devices, which happened to Schlage locks).
I am not sure if @bcopeland was able to find the specific version you have, so I'll let him provide an update on that.
P.S. if you didn't update to the latest version of the Z-Wave firmware, please do so as soon as possible. It has been confirmed to significantly improve the Z-Wave perfomance in busy environments.