I don't pretend to know why the ECOM-EX is losing comms, unless it is, for whatever reason, running out of resources somehow.
The ECOM-EX and the Built-in port BOTH use the same TCP/IP stack. The Gateway address configured for the Built-in port has priority. There cannot be two Gateway addresses. I mean, you can configure the ECOM-EX and the Built-in to have two different Gateway addresses, but only one will be used, and the Built-in has priority. The best way to think of this is one is a WAN (needs a Gateway) and the other is a LAN (doesn't need a Gateway). So, in my way of thinking of this, I would put the DMIOs on the LAN (no Gateway address needed, or configured), and the office network & HMI on the WAN (Gateway required and configured).
So, delete the Gateway address for the Built-in controlling the DMIOs, if you haven't already done so.
Now, in troubleshooting the issue:
- Monitor DST72 ($FreePackets). The value here should hover around 375. If it starts to trend downward, turn ON ST300. This will then cause DST98-399 to fill with connection data that we can take a look at.
- You can also turn ON ST301, which will cause DST200-205 to fill with values. These values might also tell point us in a particular direction as to what is happening.