Find out why a screen is black or not showing the right thing

Every cause that could explain why a screen looks wrong, most likely first: offline since a time, an empty or failed slideshow, nothing scheduled, every slide hidden by its rules, live slides waiting for their first data (WaitingForData: push data to the source), plan expired or over the device limit, or its stream token rotated (paired elsewhere). Each cause carries a sentence and, where there is a concrete next step, a ready-made fix request. A healthy screen returns no causes.