A common condition contributing to this is that layer 0 is frozen or locked.
In this case layer 0 is frozen. We thaw (unfreeze) it.
Now using the block editor we view one of the devices not displaying a label.
In the block editor we do not see the expected device attribute. We close the block editor.
Because we have thawed layer 0, we now place a device on the drawing that has not been used in this project. If we don't need it we can delete it later.
We copy the Device Attribute to our clipboard.
Now we close the block editor and use it to edit the block with the missing attribute.
We paste the Device attribute in to the block.
We press "OK"
Close the block editor and save the change
Save the change
Now we use the ATTSYNC command on the block.
Choose to select the block.
Now refresh all labels
The connected device address appears.