Off center cork grip
It sounds like the inletted bore of the cork ring was not concentric to the ring and/or the reel seat was not centered. When finished this would be the thinnest cork on the handle and minor errors could show up as you describe. While it is probably me, I do not fully understand your description of the method you used. If you would care to PM me with contact info perhaps I could talk you thru it. I build 2handers and turn all grips on the blank and have yet to have a problem like that.