I just had the exact same issue. NPC Overhaul caused the issue for me.
Go into the downloaded NPC Overhaul folder (the one that has the TSLPatcher), go into the folder named "backup", and copy the 208TEL.mod file to the "Modules" folder in your game directory, and see if that fixes your issue.
I just got through that section. Thanks for mentioning the invisible thug, I hadn't noticed him and that lead me to suspect NPC Overhaul.