A small but silly one: breaking middle and right click functionality for links.

An auction site I use loads in the list of auctions after the rest of the page loads in, and also doesn't let you open links with middle click or right click>new tab, because the anchor elements don't have href attributes. So that site is a double-dose of having to open auctions in the same tab, then going back to the list page and losing my place in the list of auctions due to the late load-in and failure to save my scroll location.

I would submit this as product feedback if you haven't. One of my favorite things as a dev working on client-facing things is when I get negative feedback that presumably has a pretty easy fix to at least part of it ("add 'href' to these links") where I can pretty quickly make someone's life a little easier.

This is not exclusive with an SPA. Even MPAs/SSR apps can have this issue. But I guess MPAs are probably not built with post load interactivity in mind and maybe that's why its less prevalent there.

This issue doesn't get enough attention; apart from the obvious implications on bad UX, I find myself losing interest in a project after realising its broken in so many subtle and non-subtle ways due to the underlying tech. I, like many others, got into programming due to the joy of creating something beautiful and attempting to follow (influencer led) JS trends nearly killed my interest in this field at a time.