A quick way to find which devices (MDTs and Repeaters) are not reporting in is to go to the Configuration Data -> Node View tab, then sort on the Icon column (the first column). This will sort the list by connection status. A binocular icon identifies a non-reporting unit. You may need to sort twice to bring the binocular icons to the top of the sorted list (each click will change the sort order between Ascending or Descending order). Note that a unit is considered non-reporting if no Reads data was seen in the data that was downloaded from the DCAP. The default download period is the last 12 hours. So if you instead download 48 hours of data for example, some units that previously were missing could appear now as OK as there was some data from that unit within the 48 hour period.
Here is the meaning of each Icon: