this happens with getClient and setClient because it is a svelte context which is only available at component initialization (construction) and cannot be in an event handler.

setContext must be called synchronously during component initialization. That is, from the root of the <script> tag

It looks like the issue stems from having "svelte" as a dependency instead of a devDependencies in package.json within the sapper project. This causes import 'svelte' to load the rollup excluded npm package's set_current_component instead of from within the sapper generated server.js.