I disagree, the problem with an SPA is that now you have two places where you manage state (the backend and the frontend). That gives you much more opportunity for the two places to disagree, and now you have bugs.
Unless you can guarantee RTT under 100ms, you have to manage some state on client side, else your UI will feel sluggish.
Client-server model is known for decades, state management between them isn’t hard.
You had to manage state on the frontend even before spa though, if you wanted anything but the most basic experience.