My guess is that the tailstock is not perfectly aligned with the headstock. This is the problem with wood lathes, which is to say you can't adjust the tailstock.
However, the larger Nova lathes have the capability to adjust their tailstock and even a tool that is basically a double ended 2MT.
I have a jet lathe that is not aligned correctly. I ended up shimming under the tailstock to bring it in line with the headstock.
Or, if your tailstock has a little play left to right, you can eyeball it and gently tighten it down while it is lined up and it might stay lined up. But my Jet doesn't have any left to right slop, so this wont work on mine.
Metal lathes have gibs which allow you to adjust it. I cant understand for the life of me why all wood lathes don't have this feature. It only makes sense...