Hi Kevin,
most likely radar interference. This is often caused for example by strong wi-fi near the radar location or some other transmitter. Such interference commonly shows up as straight lines or circular patterns. A squall line would never be this straight and never so sharp and narrow.
The radar also experiences interference from the electromagnetic energy emitted by the sun. At sunrise and sunset you will often see a spike of returned energy on the display.
It could also be a SW bug, but it is probably not so likely because the line has some gaps.
Or it could really be some very strange storm, but I have seen many radar images and never anything like this which would not be either interference or as you pointed out SW bug.