Failed to serialize preloaded data... Cannot stringify a function

[woutdp]

First of all thanks for the project, it's been very helpful!

Problem

When going to an individual blogpost, and refreshing the page so SSR gets triggered, the following warning occurs:

Failed to serialize preloaded data to transmit to the client at the /blog/<slug> route: Cannot stringify a function
The client will re-render over the server-rendered page fresh instead of continuing where it left off. See https://sapper.svelte.dev/docs#Return_value for more information

This is likely caused by:
https://github.com/ryanfiller/sapper-mdsvex-starter/blob/main/src/routes/blog/%5Bslug%5D.svelte#L15

component.default is a function and sapper doesn't know how to serialize this

Effect

This causes some styling to flash.

Reproduce

Go to https://ryanfiller-sapper-mdsvex-starter.netlify.app/blog/mdsvex/ and refresh the page, you'll see a flash where styling isn't applied.

Information

Versions

svelte: 3.35.0 
sapper: 0.29.1