Sensor Racks not Syncing to concert

Hello, we have been having issues recently where some of our Sensor 3 racks will not sync into concert, or show up in the Eos dimmer patch list.

Concert will detect them, and show they exist on the network, but is unable to pull the config from them /gets stuck with the loading bar empty or half full sometimes) However the Web interface for them still works.. 

Nodes still show up and are configurable. 

We have no clue what causes it, and I can't find any logs to look at to work this out. To fix the issues we have to reset/restart the control module in each rack.

Any ideas?