hhhmmm
your comemnts about the bed vs cot at nursery make me think perhaps he is ready for the transiotion.
However, I wouldn't normally recommend making a change when there are "sleep problems".
Sorry, not very helpful.
I will say, that my DS went through a similar stage at that age. It seems to be fairly common. Perhaps they have more complex lives now to "unwind from". Moving the bed time back 30-60 min later did help, but we still go through periods where he may take up to an hour to fall asleep, almost never crying though.