Strange issue on outside one one side and only vertically

[TTVert]

well if you already know what it's not - why ask ?

Have you tried printing the file a lot smaller ? say 25%
That way you should be able to rule out the file and usb connection.

Also we know you haven't had this problem before.
So saying 'it can't be that, i've never had this problem before' - without testing it doesn't help any of us.

Trouble shooting is a tedious process that involves ruling things out one at a time.
It's entire;y up to you whether you do it or not.

You make a very valid point. I guess the issue with making these changes and reprinting is that the print was a 17 hour print so it's not really feasible to make a change and reprint this particular job. Given the issue was starting at layer one what I will try it to print only about 20 layers of the existing job but at 1/2 scale. That'll be a 25 min. print that hopefully tells me something. If it doesn't do it at that size then i'll go up in scale to see at what scale I do end up getting the defect. I know when I printed that calibration square as a test the other day it came out perfect, although that was a fraction of the size. I guess my question would be, if I reduce the print size does that really tell us much? If it goes away by reducing size that couldn't that just be due to less distance the nozzle has to travel and therefore perhaps less time for retraction if it's in fact an excessive retraction issue?

Apologies if I ticked anyone off.

Dave