Modbus tag connect and disconnect

I have 18,000 Modbus tags using a scan class (1 minute). I turn on the history on the diagnostic tag that shows the connection status and in two hours it recorded 7 disconnections. Not sure why we are losing connection to the Modbus PLC.

Any idea?

Most Modbus devices will close incoming connections that are idle for more than 10-15 seconds. If your device is configurable in this manner then you just need to increase it. Otherwise you need to make subscribe at least one tag at a rate below the threshold where the device will close the connection.