A wallboard that shows no data, or only some of it, usually means the integration has not loaded the wallboard settings yet. This happens on new installations and right after you create a wallboard. A restart of the JEDWare service fixes it.
Debian
sudo systemctl stop JEDWare
sudo systemctl start JEDWare
Windows
In services.msc, restart JEDWare Integration. See How to restart the JEDWare service.
Why it helps
Stopping the service clears the settings held in memory and drops every wallboard connection. Starting it sends the current extension and queue lists to the JEDWare cloud and loads the wallboard settings again, so the board starts fresh with the right queues.
Still empty? Check that the queues on the board are visible to JEDWare in Admin settings, and that the integration status is not No connection (see this guide).
Want the short version? The 3CX wallboard feature page sums up every layout, the SLA alerts and the no-login share link.