Sorry no solutions but I hope things are improving for you. MY 7month old DS is exactly the same, he fights sleep. If he doesn't want to go to sleep he won't despite providing opportunities for him and he being so so tired - yawning double eye rub, girzzle the works.

I wonder if he "misses" you? You mention a Nanny so I assume you are at work. Maybe he is trying to get your attention and spend more time with you. What does the nany do differently? Is she firmer? Maybe he knows that mummy will "let" him get up or he likes any reaction it provokes from you. Does he get more kisses and cuddles and stories trying to get him to settle?
How long are his naps? Maybe he needs to consolidate them down to one or two for the day?

No doubt you have thought of these things.

Good luck