Ah, I know exactly what you mean - those frustrating intermittent communication issues where everything looks fine in the logs but you're still getting random drops! Here's what I'd suggest based on my experience:

1. Start with the physical layer - Check all network cables, connectors, and terminations. Intermittent issues often come from loose connections, damaged cables, or EMI interference. Make sure you're using industrial-grade Ethernet cables, not office-grade ones.

2. Network infrastructure check - Verify your switches are industrial-rated and properly configured. Look for broadcast storms, duplex mismatches, or spanning tree issues. Consider using managed switches with IGMP snooping enabled for EtherNet/IP networks.

3. Monitor actual network traffic - Use Wireshark or a network analyzer to capture packets during the failure. Look for retransmissions, timeouts, or unusual traffic patterns. The logs might say everything's fine, but packet captures don't lie!

4. Check RPI settings - Make sure the Requested Packet Interval (RPI) settings aren't too aggressive for your network or the third-party drive's capabilities. Try increasing the RPI to see if the issue goes away.

5. Third-party drive diagnostics - Check if the drive has its own diagnostic logs or status indicators. Sometimes the issue is on the drive side, not the ControlLogix side.

6. Power quality - Check for voltage dips, spikes, or grounding issues. Intermittent power problems can cause communication drops.

7. Try isolation testing - Temporarily connect the problematic drive directly to the controller (bypassing switches) to rule out network infrastructure issues.

The key is that intermittent issues often don't show up in standard logs - you need to look deeper at the network layer and physical connections. What type of network are you using (EtherNet/IP, DeviceNet, etc.) and what brand of third-party drives?