211 triplex

I recently got a triplex of Otis 211s and everyone and awhile non of the cars will respond to hall calls. Can give car call from controllers. The master cars “ring” led is out on the cpu board but the other two it still flashes normally. As soon as I rest master car the the ring light comes back and all all will respond to hall calls. It’s will last for a week sometime 3. Then happen again.
Any ideas?

Check the controller to controller group wiring.. there's typically a SOM, switch over module in each controller, which allows controllers to apply power to the group functions, bypassing units and pulling power from others as units loose mainline power or are shut down. There are basically two groups of wires, power and comm, going from 1-2, 2-3, 3-1, creating a loop.
If all that looks good, check the tool and ensure that each controller is labeled correctly ie; 1, 2 or 3. Ensure all code / function settings are same in each controller regarding ocs and group