Michel,
I upgraded to 5.6.4 a few days ago and I just tried the switch again now but not sure if I did it correctly...
I right clicked the device and chose the option to remove it from the zigbee network. The icon then got a red line through it for a while, but returned with the light bulb icon.... so I right clicked it again and chose the Delete option, which did get it out of the UI.
I then did a factory reset on the switch, and re-added it by clicking on Zigbee at the top of the UI and choosing 'Add Zigbee Device" It went through the interview process and added it again with the bulb icon. The device name was "ZB xxxxx.1 Unavailable" (the x's are numbers). In the UI it simply shows a 'Query' button but nothing else. I tried right clicking, choosing zigbee then 'Update' but it made no difference.
At this point i unplugged the power cable and completely rebooted my eisy.
After rebooting and logging back in, now when i select the Zigbee button, at the top are 'water alarm' and 'battery level' boxes but both are empty. Below is a 'set configuration' button, and to the right parameter number & value boxes. At the bottom there are now two buttons 'Query' and 'Write Changes'. In programs I created a test program, but the Zigbee device doesn't show in the list when I try to create an IF based on either status or control.