Offline means that the panel did not receive expected signals from the device recently, it may only be a short lived status if the issue is borderline range problems, battery levels, etc.
With Z-wave since it is a mesh network one or two issues can result in what looks like more. If one commonly relied on repeating node is experiencing trouble it can impact signaling to further devices.
The bigger your network the more reliability it should have, but it does depend a little on layout of those devices. If they are pretty evenly spread then you should see fewer issues in general.
This could be the panel signal being interrupted or weakened.
Some things to consider:
Where is the panel? Is there any large source of metal nearby? Has the panel been moved?
Have any Z-wave devices been recently added to the network shortly before this started happening?
Have any Z-wave devices been recently removed?
Are the devices the panel is reporting as offline all in the same area of the home in relation to the panel?
It looks like your panel has an available firmware update. Tty updating to 4.5.2 by the steps here: