This happen a long time ago with me and i trouble shot removing things and for me it turned out to be if two problem npcs were on that save and if you got rid of one of either those npc it would fix and to fully fix it for me i removed and remade those npcs and i haven’t had that issue.
Note i had several npcs but it was specifically 2 of them that was causing the issue i tested it and removing one of those two fixed it, i was very puzzled.