Vertical Red/Blue Lines in Trend View

[RBPLC]

What do the vertical red/blue lines in a trend view mean? For a while, I've assumed that these indicated comms issues between the PC running DmD and the PLC. I'm seeing these now in a trend view where I suspect comms to be good between the PC and the PLC but all values shown on the trend view are coming from remote Modbus devices and I'm getting periodic MRX/MWX failures. I believe the network infrastructure from the PLC to the Modbus devices to be less than ideal.   

[franji1]

They are Comm Link status, including status going on and off, which can happen during Program Writes, firmware updates, changes to the System/Memory Configuration.

Blue:
Link Error CLEARED
Link UNPAUSED (after editing a Comm Link)
Link ACTIVE (check/uncheck Link Active in Link Editor)
Status ON

Yellow:
Status OFF

Red:
Link INACTIVE
Link PAUSED (editing Comm Link)
Link ERROR (comm error)

[franji1]

To see Comm Link log details, open up the Link Info dialog either by clicking on the Link name in the Status Bar or under PLC->Link Info menu item.

[RBPLC]

I'm guessing that seeing Transport Protocol Errors (appearing "randomly" and for very brief periods of time <1/2 second) could be a sign of potential network traffic issues. I'm also guessing that seeing a timeout for a sufficiently long period of time would also indicate that the same network conditions causing the timeout of the link would cause issues with the MRX/MWX functions. Are these true statements? 

[franji1]

I'm guessing that seeing Transport Protocol Errors (appearing "randomly" and for very brief periods of time <1/2 second) could be a sign of potential network traffic issues.

Could be Noise (more likely), Runtime Edit, Firmware update.  Unless you have some kind of broadcast or bandwidth issues, noise is a potential comm issue.
Here's some general help on Ethernet, Panels, and Noise:
https://hosteng.com/FAQFiles/ECOM.htm#FAQ0045

I'm also guessing that seeing a timeout for a sufficiently long period of time would also indicate that the same network conditions causing the timeout of the link would cause issues with the MRX/MWX functions.

Network traffic, noise, runtime edit, firmware update - yes.

Realize also that there may be issues on the Designer/Modbus Client side, not necessarily the PLC side, so Modbus may be fine but Designer is not (or vice versa).  But if it is PLC side, it can affect all areas of Communication.