It could be seperation Anxiety but I also think that his nap and bedtime is a little late, it could be that he is overtired by the time naptime comes and he might fight it then, also, as his nap is cut short due to overtiredness he is still tired come bedtime, does that make sense?
I would do a nap of 12-12.30pm and then, if you can get a good 2+ hours from him do a bedtime at around 7pm, I know that it's only half an hour but it could make all the difference. You may need WIWO as he won't be usedt o the routine but as he was a good sleeper previously you should have him sleeping again soon.