pturmel

Right, that means your PLC "owns" those devices.  Most I/O devices do not permit many, or any, configuration changes while a scanner owns them.  You will need to inhibit those modules in the I/O tree to be able to write configuration attributes.

I just discovered that my Mikrotik router can do packet captures for me on selected interfaces and stream the results to a Wireshark instance on my laptop.  No need for the port mirror at all (but HW offload has to be disabled on the affected ports).

If you have to track in arrays of larger data structures, using ring buffer techniques can greatly reduce CPU utilization.  Using the shift instructions, or COP for shifting, is quite expensive.  Instead of shifting, you add to an integer subscript for the load point to manage where you are in the array.  And wrap around the end.  For physical items on the conveyor a known distance downstream from your load sensor, you simply add to the load point subscript the constant for the distance (in array elements), wrapping it around, too.

No question about that at all. But I am often not on-site, so a port mirror that can be configured remotely has great value.  And, sometimes, simply moving connectors masks a problem.

Troubleshooting problems in cases like this.  Most modern managed switches have features to help technical staff connect wireshark to specific ports, so that sources of bad behavior can be examined unfiltered, and without relying on an intermediate two-port switch. Actual DLR, though, is awesome.

Wireshark can only capture packets that arrive at the PC's physical network interface.  That often requires using a special mode on your switch to "mirror" everything to the PC's port, and ensuring that all devices are connected to the switch.  You will not be able to capture traffic from daisy-chained devices.  (The dual ports on AB devices should only be used for real rings.) The mode problem suggests that the device in question is "owned" by something.  What are these devices?  Please also show your Studio 5000 I/O device tree where Device1 and Device2 are present.

I would make it precisely to fit my needs.  Maybe Mitsu has something built-in, but I'm not a Mitsu expert.

Since the master PLC is actually a modbus slave, and you want that slave to also respond to your monitoring, you will likely need to write a regularly changing value from each slave PLC to separate registers in the master PLC (heartbeat signals).  Then have code in the master PLC that will time out if a given slave's heartbeat stops changing.  Place the booleans for that status in other modbus addresses that the monitoring system can see.  (Or, perhaps, have the monitoring system watch the same heartbeat values.)

Share more details.  What is the network topology?  Are both PLCs Allen-Bradley?  Are you using message instructions in one to talk to the other? If so, show the three tabs of a message configuration. Embedded service error indicates that a request used message router service 0x0A to embed multiple requests in a single packet, and one or more of those inner requests failed in the target device.  You would have to inspect the nested responses to determine the true error or errors.  (Wireshark will help you do that.)

I would get an IT person to help you collect a wireshark capture, to see how far the connection attempt packets get.  And therefore let you focus on where they stop.

Sounds like a ground loop / isolation failure. (I have no experience with either those PLCs nor those HMIs, but that is where I would look.  With a scope, if necessary.)

I would expect you to need to use the SLC500 driver for that one.

Which model MicroLogix?  One of the new ML8xx family?  If so, you will need to use Control/CompactLogix(Tag) mode, for access to some global variables, or assign Modbus addresses within the ML8xx program.

Failure of the flyback protection on the contactor coil often proceeds to destroy the contact surfaces in the upstream relay.  But there are many possible reasons for mechanical failures, too.  You would need to dismantle the PLC output to determine anything for sure.

USB type A, type B, type B-mini, and type B-micro are not bidirectional.  I would be shocked if you could use any adapter there to plug in a mouse.