As a user my main beef against SPA is that most of the time they break basic browser functionalities, like the ability to open links in a new tab, or using the back button. When the UI doesn’t simply break with part of the content off-screen.
That’s not a bad thing but it’s extra work which someone has to be responsible for, similar to how e.g. using a complex custom widget means you’re on the hook for accessibility rather than the browser vendors.