issue with guitar to bass {v studio 20}

hi, i just bought the v studio 20 today and im having issues with the guitar to bass function. when i play the guitar to bass the pitch shifting is all over the place and it wobbles all over the place like the vocals in a song with bad auto tune. one idea i had was the guage of strings i use may be too light making it hard to keep a solid note for the guitar to bass function. not sure. any help on this issue would be greatly appreciated because the guitar to bass function is one of the main reasons i bought this bit of gear. cheers.