I haven't seen anything like this for years... it was in the back of my mind the first time you posted your maps.    Back in the mid 90's, we had some situations where the decimal resolution of the Lon/Lat values in the GPS sentences was enhanced (as receivers started to get more accurate).   There were some field devices that could not deal properly with the enhanced resolution.   They would drop digits out right after the decimal place... so when you rolled from .19 to 2.0, the monitor thought you were rolling from .9 to .0, obviously creating a very big jump.    You effectively ended up with chunks of data separated by white space.

How can you verify?   Well, in your software, can you hover the mouse or click on the screen and see what the software thinks the lon/lat is?   And does that match up with what you know it to be?    Have you tried displaying county roads or background maps to see if any of the data is even close to in the right place?   That's where I would start.

Whatever is going on... I'm pretty sure it is something with your GPS receiver.   Either it is configured in a really weird way, or the firmware in your monitor is not set to handle the format that is being sent to it...  that my guess, anyway.    Did you ever say what the monitor was, version, age, etc?   Or the GPS?

If you want to e-mail me the card, I can run it though our software, place it on imagery, etc, if you can't do it with your software.