It looks like there's a bug on SLG (and in the K-BB UI), but it's really just an "Actual" and "Actual Per/162" line as the players from 2020 really distorted the rate statistics in terms of the actual stat line in the draft center compared to what your team line looked like on your team page once in a league. You could see AVG/OAV swing by 10 points, ERA/WHIP/HR9, etc also swing significantly... this was put in to give better understanding of how the shorter seasons impact those numbers once they get prorated to 162