I have a few questions:
1.In Homey Developer Tool, when I display devices in the z-wave network, two devices are visible as Offline. The devices are working properly. Why are they shown as Offline?
No it resets your z-wave network to factory defaults.
So you can start adding devices again.
how rebuild the Z-Wave network?
Options:
a] Mark down old device ID, reset ZWAVE, re-add all devices, fix your flow using [HOW-TO][Pro][Cloud] - Tool to FIX (advanced) flows after removing and re-adding devices
b] Reset ZWAVE, re-add all devices, fix your flows manually
Have a couple of Zwave battery devices myself, and they have always been offline.
Worked just fine since installed. They are just sleeping/saving battery, and only wake up every 15 min to report sensor data.
but mine when wake up, the “Offline” status is still shown.
What is the difference between your 2 “multisensor 7” devices, as shown in your picture? 1 runs on battery, the other on mains?
yes, one Multisensor on battery and the other Multisensor powered by USB.
The “wake up” time for most battery-operated devices is only few seconds long. In order for to be displayed as “online”, the DevTools page would have to be refreshed during this short time. My recommendation: do not worry about it.
You have to delete Z-Wave devices via smartphone or Web app. The “Remove” option in DevTools is only active if the device no longer has a connection to the Z-Wave network or is an unknown device/NodeID.
There is a trick to make “Remove” option became available. Just click on “Test” option first, and “Remove” will be enabled 
This shouldn’t actually be the case if the Z-Wave device has a stable connection. I’ve just clicked on “Test” 10 times, but “Remove” didn’t become active.
If the “Test” fails, then “Remove” is activated, that’s right.
Tested on HP23
I checked it on a several battery powered devices, and it always work, as the battery powered devices cannot respond on demand. And like you said, it will not work on non-battery powered devices, if this device has stable connection.
Yes of course, this works with battery-operated devices because they cannot send test data to Homey if they have not been woken up first. So in this case they are not reachable for Homey.
