The shoes are the most difficult clothing items to fit on G8. The main reason is that the bone structure in the feet/ankle has been deeply changed at genesis 8. Sometimes, autofit or the converters works, sometimes, they don't.
If the conversion fails, I generally try an alternative method from SickleYield. The basic idea is to try to fit the shoes without autofitting or even parenting them to the G8 char. Just move the shoes/feet until the fitting seems correct. Them use "transfer rigging" and voila. See this post for details https://www.deviantart.com/sickleyield/art/A-Reminder-on-Autofitting-Shoes-to-Genesis-2-or-3-412985230
I have got some success with this method to fit to g8 some shoes that could not be autofitted. But, TBH, I have also got a comparable number of failures :(.