Checkerboard Skin

Hi, thanks for the reply. 
Tried the "vanilla" test and the glitches were 'mostly' gone - for some reason the feet/ankles still have glitches. The skin also appears to be somewhat darker than previously. 
This Sim was originally a NPC spawned by the game, whom I then gave a general 'makeover' (hair, eyebrows, eyelashes, arm- & leg hair, clothes) and added to an existing household. I may have lightened/darkened the skin slightly (don't really remember) with the in-game Skin Tone Menu, but I don't actively use any skin overlays or CC skin tones. Having said that..... I did actually find some skin tone CC in the Mods folder, which I must have accidentally obtained by downloading CC outfits. However, they have all been banned to a folder on my Desktop and the glitches still appear.
By-the-by, all of the NPCs spawned by the game are taken only from my Library (MCCC Population Settings, set to Import Tray Settings 100%) and those Sims were all downloaded from the gallery. 

As mentioned in my first message: with Mods/CC in place, the glitch appears only in my main save/game, but not in either the second or third save/game (also with Mods/CC). As such, I can't get away from the idea that the problem must have something to do with this one particular save/game and not the Mods/CC as such. Perhaps the up-date 'mid-game' threw a wrench into this particular save's coding.........???