Where can messages hide for a while?

This is in a factory setting:

We have an Omron mobile robot which communicates with an Omron PLC via our building's wireless network.

In one operation, the robot will send a message over the wireless connection when it arrives at a specific point.

The PLC is listening to the data stream, recognizes that message, and sends a return message.

The robot logs the time of its outgoing message and when it receives the reply.

Typically these log entries are 0.3 seconds apart.

However, recently the robot has become significantly less responsive (to the point it's unusable).

In looking at the log, I see one instance where the log entries are over 2 minutes apart.

Any ideas where (robot, PLC, network) one or the other of those messages could hang out for that long?

I don't have any details of what communications hardware is in the robot - I do have a tech request in with them, but they tend

to be slow responding.

Our IT guys say it can't be in the network, but that's the usual response . . . 

PLC's generally react very quickly, and there's nothing else happening with it, so I don't believe it's responsible.

Hello and welcome to BC:

Have you tried Omron support?

This is the US site - you will likely find a similar page for your locale if you are not in the US.

https://automation.omron.com/en/us/services/technical-support

I have a question in to their tech support, but they tend to be a bit slow to respond, then they want the log file from the robot, which is too large to send by email, so it takes my IT group almost a week to set up the ftp server so they can get it, then I have to wait for them to look at it and respond  . . . . . .

Figure I can do some research in the meantime to see if anyone can help me figure out the right direction to point.

During this whole project, we've fought a number of communications issues, have gotten a lot of support from Omron.

Typically we find a problem, our IT group says it must be Omron's equipment, then we go through a lot of testing which finally proves it's an issue with our network, then IT fixes it.

This may end up being the same - which is why I'm looking to see if anyone can tell me where in the system a message could hang out for a couple minutes before being delivered.