NextJS - Icons as slots don't appear to SSR

[jamieomaguire]

It seems as though our Icon web components do not properly render when SSR is used in the NextJS app. From some basic testing, I can only see this issue occurring when icons are used as slots. When they are used on their own, or inside another component, they seem to render fine.

To reproduce:

1. Go to the Icon Button page for the NextJS app.
2. In the browser tools (I recommend Chrome), disable Javascript
3. Reload the page
4. The Icon button will render, but there is no icon inside it

Expected behaviour:

1. Go to the Icon Button page for the Nuxt app.
2. In the browser tools (I recommend Chrome), disable Javascript
3. Reload the page
4. The Icon button will render and show the icon inside it

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In contrast, the icons page for NextJS seems absolutely fine using the approach above to test.

I have tried using other web components as slots and they seemed fine. I also reproduced this by adding both pie-divider and icon-search to the pie-card component on the card page and only the icon did not render.

[jamieomaguire]

Further info - it seems like when I run a proof of concept using NextJS 14 and the App Router structure, the issue does not exist.