In regards to your question:
"We are using HMS-EN2MB-R to communicate with Honeywell Slate Modbus TCP to our ControlLogix L73 PLC.
Is there a way to detect the modbus communication not working / freezing.
We had this happen a few times and we couldn’t detect it. We had to turn and off the HMS in order to communicate with the Slate again."
I would take a look at the section in the User Manual that deals with the Control/Status Word, Live List, and Transaction Status List. These allow you to retrieve the status of the device over the network and could be used to alert you if something was wrong:
Please let me know if you have any questions about it.