Just wanted to offer some (((HUGS!)))
I'm sure everything will get straightened out with his sleep soon. I know how frustrating it can be. My dd is 21 months old. When I read your post, my first thought was teething. My lo is also a great sleeper. Never fights nap or bedtime. BUT when she started getting her molars, things got very rocky. I would have to sit by her bed until she feel asleep. Each time, this would last about a week, and then she would go right back to her normal routine and I could just leave after saying goodnight. So, I would definitely treat for teething if you think it might be an issue, and then, maybe just give him that little extra time in his room to soothe him. I really worried at first about it becoming a habit for her, for me to stay in the room with her, but since she had such an established routine before, it didn't become a problem. As soon as the teeth quit bothering her, she knew how to soothe herself. Don't know if that will help, but just wanted to offer any suggestions I could that might be helpful!
Good Luck! I'm sure things will get back to normal soon!