In case other attempt did not get the info seen, the bug as I've observed it appears to be with the "stat_use_multiplier" tuning when used in conjunction with visible Skills (e.g. skills that can show up in the Skills UI panel). The behavior is that if the sim has a buff containing "stat_use_multiplier" for a visible skill for long enough, that skill will be added to the Skills panel even if no progress has been made on it. To ensure it's not just mods, I tested this behavior using the Back Pocket Observatory to get a sim into a focused mood with mods disabled (the base focused buff has a multiplier for Charisma and Video Gaming skill, buff: MoodBuff_Hidden_Focused, 12839); eventually, Charisma and Video Gaming appeared in the sim's Skill panel, in spite of the sim having no progress in either skill.
My hypothesis is that something to do with the skill/statistic tracker has gotten tangled with the "stat_use_multiplier" tuning, causing the tracker to periodically look through buffs on the sim and add skills to the tracker if they are part of a "stat_use_multiplier" tuning, but I don't have anything to confirm that, just offering it as a possible angle for them look at.
Edit: Also worth noting, at some point the behavior changed slightly to where the skills mistakenly added to the UI don't appear until a reload (maybe traveling too, I did not test that). So if you are attempting to reproduce, you may need to trigger the behavior and then save and reload to see the skills appear in the UI.
