Suddenly hates the pram?

Hi! Any advice appreciated. My 5month old suddenly hates going out in the pram. He used to love it, and we would do 1.5hr-2hr walks a day where he would happily nap or watch the world go by. I changed to the pushchair seat, and even got a new pram with a more comfortable pushchair seat, but he hates it when we are out on a walk. He will sit in it when we are stopped quite happily but once we move he kicks off and works himself into a state. He will play with a toy to distract him for a minute but quickly starts crying again. As soon as he's lifted out he is smiling and happy as though nothing was the matter 🫠 I've had to take the carrier the last few walks and swap him into that halfway as he is so upset in the pram. I switched it to world facing on the last walk and that helped for a bit, but then he got upset again. It's such a sudden switch in him hating it i don't understand why? Does anyone have any advice on how I can help him enjoy his pram again? I miss my peaceful relaxing walks 😅