Glad I found this thread... though no fixes it seems x.x
Just to add my info, have played since about the 20th of December without this issue at all, then it just appeared today, Jan 17th. I am on PC and had just installed a few mods today and tried a character editor so thought it had to do with that. Deleted the mods, they were all clothing mods and had changed one save file with CyberCATt save editor for transferring appearances.
Now though with everything deleted all my saves seem to have this same issue of gray spots around shoulders on any shirt you can see skin there, but is fine when you take them off or replace with long sleeve.
Seeing all these other posts doubting now it was any of the mods since no one else has mentioned any, but am unsure what the cause is now or what to do.
Hopefully will be resolved soon, or if i find a fix will update here.