Basically I was building on 2 merged plots but in the end I didn't like my plot so I did /plot clear so I could have 2 plots each one for different things and this happened
I remember this from a while back, was a plot squared clear issue which resets the plots to its original state (including the road). It use to not allow you to then build on that section... are you able to build on it and let us know if the issue is not resolved.